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5
RELEASENOTES.rst
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@ -35,6 +35,11 @@ Virtual Machine Image Guide
* RST conversion finished. * RST conversion finished.
Architecture Design Guide
-------------------------
* Completed RST conversion.
Translations Translations
------------ ------------

2
doc-tools-check-languages.conf
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@ -30,9 +30,9 @@ declare -A SPECIAL_BOOKS=(
["networking-guide"]="RST" ["networking-guide"]="RST"
["user-guide"]="RST" ["user-guide"]="RST"
["user-guide-admin"]="RST" ["user-guide-admin"]="RST"
["arch-design"]="RST"
# Skip in-progress guides # Skip in-progress guides
["contributor-guide"]="skip" ["contributor-guide"]="skip"
["arch-design-rst"]="skip"
["config-ref-rst"]="skip" ["config-ref-rst"]="skip"
# This needs special handling, handle it with the RST tools. # This needs special handling, handle it with the RST tools.
["common-rst"]="RST" ["common-rst"]="RST"

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doc/arch-design/bk-openstack-arch-design.xml
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<?xml version="1.0" encoding="UTF-8"?>
<book xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="openstack-arch-design">
<title>OpenStack Architecture Design Guide</title>
<?rax title.font.size="28px" subtitle.font.size="28px"?>
<titleabbrev>Architecture Guide</titleabbrev>
<info>
<author>
<personname>
<firstname/>
<surname/>
</personname>
<affiliation>
<orgname>OpenStack Foundation</orgname>
</affiliation>
</author>
<copyright>
<year>2014</year>
<year>2015</year>
<holder>OpenStack Foundation</holder>
</copyright>
<releaseinfo>current</releaseinfo>
<productname>OpenStack</productname>
<pubdate/>
<legalnotice role="apache2">
<annotation>
<remark>Copyright details are filled in by the
template.</remark>
</annotation>
</legalnotice>
<legalnotice role="cc-by">
<annotation>
<remark>Remaining licensing details are filled in by
the template.</remark>
</annotation>
</legalnotice>
<abstract>
<para>To reap the benefits of OpenStack, you should
plan, design, and architect your cloud properly,
taking user's needs into account and understanding the
use cases.</para>
</abstract>
</info>
<!-- Chapters are referred from the book file through these
include statements. You can add additional chapters using
these types of statements. -->
<xi:include href="../common/ch_preface.xml"/>
<xi:include href="ch_introduction.xml"/>
<xi:include href="ch_legal-security-requirements.xml"/>
<xi:include href="ch_generalpurpose.xml"/>
<xi:include href="ch_compute_focus.xml"/>
<xi:include href="ch_storage_focus.xml"/>
<xi:include href="ch_network_focus.xml"/>
<xi:include href="ch_multi_site.xml"/>
<xi:include href="ch_hybrid.xml"/>
<xi:include href="ch_massively_scalable.xml"/>
<xi:include href="ch_specialized.xml"/>
<xi:include href="ch_references.xml"/>
<xi:include href="../common/app_support.xml"/>
<glossary role="auto"/>
</book>

45
doc/arch-design/ch_compute_focus.xml
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@ -1,45 +0,0 @@
<?xml version="1.0" encoding="UTF-8"?>
<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="compute_focus">
<title>Compute focused</title>
<para>Compute-focused clouds are a specialized subset of the general purpose
OpenStack cloud architecture. A compute-focused cloud specifically supports
compute intensive workloads.</para>
<note>
<para>Compute intensive workloads may be CPU intensive, RAM intensive,
or both; they are not typically storage or network intensive.</para>
</note>
<para>Compute-focused workloads may include the following use cases:</para>
<itemizedlist>
<listitem>
<para>High performance computing (HPC)</para>
</listitem>
<listitem>
<para>Big data analytics using Hadoop or other distributed data
stores</para>
</listitem>
<listitem>
<para>Continuous integration/continuous deployment (CI/CD)</para>
</listitem>
<listitem>
<para>Platform-as-a-Service (PaaS)</para>
</listitem>
<listitem>
<para>Signal processing for network function virtualization (NFV)</para>
</listitem>
</itemizedlist>
<note>
<para>A compute-focused OpenStack cloud does not typically use raw block storage
services as it does not host applications that require
persistent block storage.</para>
</note>
<xi:include href="compute_focus/section_tech_considerations_compute_focus.xml"/>
<xi:include href="compute_focus/section_operational_considerations_compute_focus.xml"/>
<xi:include href="compute_focus/section_architecture_compute_focus.xml"/>
<xi:include href="compute_focus/section_prescriptive_examples_compute_focus.xml"/>
</chapter>

95
doc/arch-design/ch_generalpurpose.xml
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@ -1,95 +0,0 @@
<?xml version="1.0" encoding="UTF-8"?>
<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="generalpurpose">
<title>General purpose</title>
<para>An OpenStack general purpose cloud is often considered a
starting point for building a cloud deployment. They are designed
to balance the components and do not emphasize any particular aspect
of the overall computing environment.
Cloud design must give equal weight to the compute, network, and
storage components. General purpose clouds are
found in private, public, and hybrid environments, lending
themselves to many different use cases.
</para>
<note>
<para>
General purpose clouds are homogeneous deployments. They are
not suited to specialized environments or edge case situations.
</para>
</note>
<para>
Common uses of a general purpose cloud include:
</para>
<itemizedlist>
<listitem>
<para>
Providing a simple database
</para>
</listitem>
<listitem>
<para>
A web application runtime environment
</para>
</listitem>
<listitem>
<para>
A shared application development platform
</para>
</listitem>
<listitem>
<para>
Lab test bed
</para>
</listitem>
</itemizedlist>
<para>Use cases that benefit from scale-out rather than scale-up approaches
are good candidates for general purpose cloud architecture.
</para>
<para>A general purpose cloud is designed to have a range of potential
uses or functions; not specialized for specific use cases. General
purpose architecture is designed to address 80% of potential use
cases available. The infrastructure, in itself, is a specific use case,
enabling it to be used as a base model for the design process.
General purpose clouds are designed to be platforms that are suited
for general purpose applications.</para>
<para>General purpose clouds are limited to the most basic
components, but they can include additional resources such
as:</para>
<itemizedlist>
<listitem>
<para>Virtual-machine disk image library</para>
</listitem>
<listitem>
<para>Raw block storage</para>
</listitem>
<listitem>
<para>File or object storage</para>
</listitem>
<listitem>
<para>Firewalls</para>
</listitem>
<listitem>
<para>Load balancers</para>
</listitem>
<listitem>
<para>IP addresses</para>
</listitem>
<listitem>
<para>Network overlays or virtual local area networks
(VLANs)</para>
</listitem>
<listitem>
<para>Software bundles</para>
</listitem>
</itemizedlist>
<xi:include href="generalpurpose/section_user_requirements_general_purpose.xml"/>
<xi:include href="generalpurpose/section_tech_considerations_general_purpose.xml"/>
<xi:include href="generalpurpose/section_operational_considerations_general_purpose.xml"/>
<xi:include href="generalpurpose/section_architecture_general_purpose.xml"/>
<xi:include href="generalpurpose/section_prescriptive_example_general_purpose.xml"/>
</chapter>

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doc/arch-design/ch_hybrid.xml
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@ -1,59 +0,0 @@
<?xml version="1.0" encoding="UTF-8"?>
<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="hybrid">
<title>Hybrid</title>
<para>A <glossterm baseform="hybrid cloud">hybrid cloud</glossterm> design
is one that uses more than one cloud. For example, designs that use
both an OpenStack-based private cloud and an OpenStack-based public
cloud, or that use an OpenStack cloud and a non-OpenStack cloud,
are hybrid clouds.</para>
<para><glossterm baseform="bursting">Bursting</glossterm> describes the
practice of creating new instances in an external cloud to alleviate
capacity issues in a private cloud.</para>
<itemizedlist>
<title>Example scenarios suited to hybrid clouds</title>
<listitem>
<para>Bursting from a private cloud to a public
cloud</para>
</listitem>
<listitem>
<para>Disaster recovery</para>
</listitem>
<listitem>
<para>Development and testing</para>
</listitem>
<listitem>
<para>Federated cloud, enabling users to choose resources
from multiple providers</para>
</listitem>
<listitem>
<para>Supporting legacy systems as they transition to the
cloud</para>
</listitem>
</itemizedlist>
<para>Hybrid clouds interact with systems that are outside
the control of the private cloud administrator, and require careful
architecture to prevent conflicts with hardware, software,
and APIs under external control.</para>
<para>The degree to which the architecture is OpenStack-based
affects your ability to accomplish tasks with native
OpenStack tools. By definition, this is a situation in which
no single cloud can provide all of the necessary
functionality. In order to manage the entire system, we recommend
using a cloud management platform (CMP).</para>
<para>There are several commercial and open source CMPs available,
but there is no single CMP that can address all needs in all scenarios,
and sometimes a manually-built solution is the best option.
This chapter includes discussion of using CMPs for managing a hybrid
cloud.</para>
<xi:include href="hybrid/section_user_requirements_hybrid.xml"/>
<xi:include href="hybrid/section_tech_considerations_hybrid.xml"/>
<xi:include href="hybrid/section_operational_considerations_hybrid.xml"/>
<xi:include href="hybrid/section_architecture_hybrid.xml"/>
<xi:include href="hybrid/section_prescriptive_examples_hybrid.xml"/>
</chapter>

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doc/arch-design/ch_introduction.xml
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@ -1,18 +0,0 @@
<?xml version="1.0" encoding="UTF-8"?>
<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="introduction">
<title>Introduction</title>
<para><glossterm>OpenStack</glossterm> is a fully-featured, self-service
cloud. This book takes you through some of the considerations you have to make
when designing your cloud.</para>
<xi:include href="introduction/section_intended_audience.xml"/>
<xi:include href="introduction/section_how_this_book_is_organized.xml"/>
<xi:include href="introduction/section_how_this_book_was_written.xml"/>
<xi:include href="introduction/section_methodology.xml"/>
</chapter>

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doc/arch-design/ch_legal-security-requirements.xml
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<?xml version="1.0" encoding="UTF-8"?>
<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="security-legal-requirements">
<?dbhtml stop-chunking?>
<title>Security and legal requirements</title>
<para>This chapter discusses the legal and security requirements you
need to consider for the different OpenStack scenarios.</para>
<section xml:id="legal-requirements">
<title>Legal requirements</title>
<para>Many jurisdictions have legislative and regulatory
requirements governing the storage and management of data in
cloud environments. Common areas of regulation include:</para>
<itemizedlist>
<listitem>
<para>Data retention policies ensuring storage of
persistent data and records management to meet data
archival requirements.</para>
</listitem>
<listitem>
<para>Data ownership policies governing the possession and
responsibility for data.</para>
</listitem>
<listitem>
<para>Data sovereignty policies governing the storage of
data in foreign countries or otherwise separate
jurisdictions.</para>
</listitem>
<listitem>
<para>Data compliance policies governing certain types of
information needing to reside in certain locations due to
regulatory issues - and more importantly, cannot reside in
other locations for the same reason.</para>
</listitem>
</itemizedlist>
<para>Examples of such legal frameworks include the <link
xlink:href="http://ec.europa.eu/justice/data-protection/">data
protection framework</link> of the European Union and the
requirements of the <link
xlink:href="http://www.finra.org/Industry/Regulation/FINRARules/">
Financial Industry Regulatory Authority</link> in the United
States. Consult a local regulatory body for more information.
</para>
</section>
<section xml:id="security-overview">
<title>Security</title>
<para>When deploying OpenStack in an enterprise as a private
cloud, despite activating a firewall and binding
employees with security agreements, cloud architecture
should not make assumptions about safety and protection.
In addition to considering the users, operators, or administrators
who will use the environment, consider also negative or hostile users who
would attack or compromise the security of your deployment regardless
of firewalls or security agreements.</para>
<para>Attack vectors increase further in a public facing OpenStack
deployment. For example, the API endpoints and the
software behind it become vulnerable to hostile
entities attempting to gain unauthorized access or prevent access
to services. This can result in loss of reputation and you must
protect against it through auditing and appropriate
filtering.</para>
<para>It is important to understand that user authentication
requests encase sensitive information such as user names,
passwords, and authentication tokens. For this reason, place
the API services behind hardware that performs SSL termination.</para>
<warning>
<para>Be mindful of consistency when utilizing third party
clouds to explore authentication options.</para>
</warning>
</section>
<section xml:id="security-domains">
<title>Security domains</title>
<para>A security domain comprises users, applications, servers or
networks that share common trust requirements and expectations
within a system. Typically, security domains have the same
authentication and authorization requirements and users.</para>
<para>You can map security domains individually to the
installation, or combine them. For example, some
deployment topologies combine both guest and data domains onto
one physical network. In other cases these networks
are physically separate. Map out the security domains against
specific OpenStack topologies needs. The domains and their trust requirements
depend on whether the cloud instance is public, private, or
hybrid.</para>
<simplesect>
<title>Public security domains</title>
<para>The public security domain is an untrusted area of
the cloud infrastructure. It can refer to the internet as a
whole or simply to networks over which the user has no
authority. Always consider this domain untrusted. For example,
in a hybrid cloud deployment, any information traversing
between and beyond the clouds is in the public domain and
untrustworthy.</para>
</simplesect>
<simplesect>
<title>Guest security domains</title>
<para>Typically used for compute instance-to-instance traffic, the
guest security domain handles compute data generated by
instances on the cloud but not services that support the
operation of the cloud, such as API calls. Public cloud
providers and private cloud providers who do not have
stringent controls on instance use or who allow unrestricted
internet access to instances should consider this domain to be
untrusted. Private cloud providers may want to consider this
network as internal and therefore trusted only if they have
controls in place to assert that they trust instances and all
their tenants.</para>
</simplesect>
<simplesect>
<title>Management security domains</title>
<para>The management security domain is where services interact.
The networks in this domain transport confidential data such as configuration
parameters, user names, and passwords. Trust this domain when it is
behind an organization's firewall in deployments.</para>
</simplesect>
<simplesect>
<title>Data security domains</title>
<para>The data security domain is concerned primarily with
information pertaining to the storage services within
OpenStack. The data that crosses this network has integrity and
confidentiality requirements. Depending on the type of deployment there
may also be availability requirements. The trust level of this network
is heavily dependent on deployment decisions and does not have a default
level of trust.</para>
</simplesect>
</section>
<section xml:id="hypervisor-security">
<title>Hypervisor-security</title>
<para>The hypervisor also requires a security assessment. In a
public cloud, organizations typically do not have control
over the choice of hypervisor. Properly securing your
hypervisor is important. Attacks made upon the
unsecured hypervisor are called a
<firstterm>hypervisor breakout</firstterm>.
Hypervisor breakout describes the event of a
compromised or malicious instance breaking out of the resource
controls of the hypervisor and gaining access to the bare
metal operating system and hardware resources.</para>
<para>There is not an issue if the security of instances is not important.
However, enterprises need to avoid vulnerability. The only way to
do this is to avoid the situation where the instances are running
on a public cloud. That does not mean that there is a
need to own all of the infrastructure on which an OpenStack
installation operates; it suggests avoiding situations in which
sharing hardware with others occurs.</para>
</section>
<section xml:id="security-baremetal">
<title>Baremetal security</title>
<para>There are other services worth considering that provide a
bare metal instance instead of a cloud. In other cases, it is
possible to replicate a second private cloud by integrating
with a private Cloud-as-a-Service deployment. The
organization does not buy the hardware, but also does not share
with other tenants. It is also possible to use a provider that
hosts a bare-metal public cloud instance for which the
hardware is dedicated only to one customer, or a provider that
offers private Cloud-as-a-Service.</para>
<important>
<para>Each cloud implements services differently.
What keeps data secure in one
cloud may not do the same in another. Be sure to know the
security requirements of every cloud that handles the
organization's data or workloads.</para>
</important>
<para>More information on OpenStack Security can be found in the
<link xlink:href="http://docs.openstack.org/security-guide"><citetitle>OpenStack
Security Guide</citetitle></link>.</para>
</section>
<section xml:id="networking-security">
<title>Networking Security</title>
<para>Consider security implications and requirements before designing the
physical and logical network topologies. Make sure that the networks are
properly segregated and traffic flows are going to the correct
destinations without crossing through locations that are undesirable.
Consider the following example factors:</para>
<itemizedlist>
<listitem>
<para>Firewalls</para>
</listitem>
<listitem>
<para>Overlay interconnects for joining separated tenant networks</para>
</listitem>
<listitem>
<para>Routing through or avoiding specific networks</para>
</listitem>
</itemizedlist>
<para>How networks attach to hypervisors can expose security
vulnerabilities. To mitigate against exploiting hypervisor breakouts,
separate networks from other systems and schedule instances for the
network onto dedicated compute nodes. This prevents attackers
from having access to the networks from a compromised instance.</para>
</section>
<section xml:id="security-multi-site">
<title>Multi-site security</title>
<para>Securing a multi-site OpenStack installation brings
extra challenges. Tenants may expect a tenant-created network
to be secure. In a multi-site installation the use of a
non-private connection between sites may be required. This may
mean that traffic would be visible to third parties and, in
cases where an application requires security, this issue
requires mitigation. In these instances, install a VPN or
encrypted connection between sites to conceal sensitive traffic.</para>
<para>Another security consideration with regard to multi-site
deployments is Identity. Centralize authentication within a
multi-site deployment. Centralization provides a
single authentication point for users across the deployment,
as well as a single point of administration for traditional
create, read, update, and delete operations. Centralized
authentication is also useful for auditing purposes because
all authentication tokens originate from the same
source.</para>
<para>Just as tenants in a single-site deployment need isolation
from each other, so do tenants in multi-site installations.
The extra challenges in multi-site designs revolve around
ensuring that tenant networks function across regions.
OpenStack Networking (neutron) does not presently support
a mechanism to provide this functionality, therefore an
external system may be necessary to manage these mappings.
Tenant networks may contain sensitive information requiring
that this mapping be accurate and consistent to ensure that a
tenant in one site does not connect to a different tenant in
another site.</para>
</section>
<section xml:id="openstack-components-multi-site">
<title>OpenStack components</title>
<para>Most OpenStack installations require a bare minimum set of
pieces to function. These include OpenStack Identity
(keystone) for authentication, OpenStack Compute
(nova) for compute, OpenStack Image service (glance) for image
storage, OpenStack Networking (neutron) for networking, and
potentially an object store in the form of OpenStack Object
Storage (swift). Bringing multi-site into play also demands extra
components in order to coordinate between regions. Centralized
Identity service is necessary to provide the single authentication
point. Centralized dashboard is also recommended to provide a
single login point and a mapped experience to the API and CLI
options available. If needed, use a centralized Object Storage service,
installing the required swift proxy service alongside the Object
Storage service.</para>
<para>It may also be helpful to install a few extra options in
order to facilitate certain use cases. For instance,
installing DNS service may assist in automatically generating
DNS domains for each region with an automatically-populated
zone full of resource records for each instance. This
facilitates using DNS as a mechanism for determining which
region would be selected for certain applications.</para>
<para>Another useful tool for managing a multi-site installation
is Orchestration (heat). The Orchestration service
allows the use of templates to define a set of instances to
be launched together or for scaling existing sets. It can
set up matching or differentiated groupings based on
regions. For instance, if an application requires an equally
balanced number of nodes across sites, the same heat template
can be used to cover each site with small alterations to only
the region name.</para>
</section>
</chapter>

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doc/arch-design/ch_massively_scalable.xml
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@ -1,79 +0,0 @@
<?xml version="1.0" encoding="UTF-8"?>
<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="massively_scalable">
<title>Massively scalable</title>
<para>A massively scalable architecture is a cloud
implementation that is either a very large deployment, such as
a commercial service provider might build, or
one that has the capability to support user requests for large
amounts of cloud resources.</para>
<para>An example is an infrastructure in which requests to service
500 or more instances at a time is common. A massively scalable
infrastructure fulfills such a request without exhausting the
available cloud infrastructure resources. While the high capital
cost of implementing such a cloud architecture means that it
is currently in limited use, many organizations are planning
for massive scalability in the future.</para>
<para>A massively scalable OpenStack cloud design presents a
unique set of challenges and considerations. For the most part
it is similar to a general purpose cloud architecture, as it
is built to address a non-specific range of potential use
cases or functions. Typically, it is rare that particular
workloads determine the design or configuration of massively
scalable clouds. The massively scalable cloud is most often
built as a platform for a variety of workloads. Because private
organizations rarely require or have the resources for them,
massively scalable OpenStack clouds are generally built as
commercial, public cloud offerings.</para>
<para>Services provided by a massively scalable OpenStack cloud
include:</para>
<itemizedlist>
<listitem>
<para>Virtual-machine disk image library</para>
</listitem>
<listitem>
<para>Raw block storage</para>
</listitem>
<listitem>
<para>File or object storage</para>
</listitem>
<listitem>
<para>Firewall functionality</para>
</listitem>
<listitem>
<para>Load balancing functionality</para>
</listitem>
<listitem>
<para>Private (non-routable) and public (floating) IP
addresses</para>
</listitem>
<listitem>
<para>Virtualized network topologies</para>
</listitem>
<listitem>
<para>Software bundles</para>
</listitem>
<listitem>
<para>Virtual compute resources</para>
</listitem>
</itemizedlist>
<para>Like a general purpose cloud, the instances deployed in a
massively scalable OpenStack cloud do not necessarily use
any specific aspect of the cloud offering (compute, network,
or storage). As the cloud grows in scale, the number of
workloads can cause stress on all the cloud
components. This adds further stresses to supporting
infrastructure such as databases and message brokers. The
architecture design for such a cloud must account for these
performance pressures without negatively impacting user
experience.</para>
<xi:include href="massively_scalable/section_user_requirements_massively_scalable.xml"/>
<xi:include href="massively_scalable/section_tech_considerations_massively_scalable.xml"/>
<xi:include href="massively_scalable/section_operational_considerations_massively_scalable.xml"/>
</chapter>

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doc/arch-design/ch_multi_site.xml
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<?xml version="1.0" encoding="UTF-8"?>
<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="multi_site">
<title>Multi-site</title>
<para>OpenStack is capable of running in a multi-region
configuration. This enables some parts of OpenStack to
effectively manage a group of sites as a single cloud.</para>
<para>Some use cases that might indicate a need for a multi-site
deployment of OpenStack include:</para>
<itemizedlist>
<listitem>
<para>An organization with a diverse geographic
footprint.</para>
</listitem>
<listitem>
<para>Geo-location sensitive data.</para>
</listitem>
<listitem>
<para>Data locality, in which specific data or
functionality should be close to users.</para>
</listitem>
</itemizedlist>
<xi:include href="multi_site/section_user_requirements_multi_site.xml"/>
<xi:include href="multi_site/section_tech_considerations_multi_site.xml"/>
<xi:include href="multi_site/section_operational_considerations_multi_site.xml"/>
<xi:include href="multi_site/section_architecture_multi_site.xml"/>
<xi:include href="multi_site/section_prescriptive_examples_multi_site.xml"/>
</chapter>

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<?xml version="1.0" encoding="UTF-8"?>
<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="network_focus">
<title>Network focused</title>
<para>All OpenStack deployments depend on network communication in order
to function properly due to its service-based nature. In some cases,
however, the network elevates beyond simple
infrastructure. This chapter discusses architectures that are more
reliant or focused on network services. These architectures depend
on the network infrastructure and require
network services that perform reliably in order to satisfy user and
application requirements.</para>
<para>Some possible use cases include:</para>
<variablelist>
<varlistentry>
<term>Content delivery network</term>
<listitem>
<para>This includes streaming video, viewing photographs, or
accessing any other cloud-based data repository distributed to
a large number of end users. Network configuration affects
latency, bandwidth, and the distribution of instances. Therefore,
it impacts video streaming. Not all video streaming is
consumer-focused. For example, multicast videos (used for media,
press conferences, corporate presentations, and web conferencing
services) can also use a content delivery network.
The location of the video repository and its relationship to end
users affects content delivery. Network throughput of the back-end
systems, as well as the WAN architecture and the cache methodology,
also affect performance.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Network management functions</term>
<listitem>
<para>Use this cloud to provide network service functions built to
support the delivery of back-end network services such as DNS,
NTP, or SNMP.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Network service offerings</term>
<listitem>
<para>Use this cloud to run customer-facing network tools to
support services. Examples include VPNs, MPLS private networks,
and GRE tunnels.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Web portals or web services</term>
<listitem>
<para>Web servers are a common application for cloud services,
and we recommend an understanding of their network requirements.
The network requires scaling out to meet user demand and deliver
web pages with a minimum latency. Depending on the details of
the portal architecture, consider the internal east-west and
north-south network bandwidth.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>High speed and high volume transactional systems</term>
<listitem>
<para>
These types of applications are sensitive to network
configurations. Examples include financial systems,
credit card transaction applications, and trading and other
extremely high volume systems. These systems are sensitive
to network jitter and latency. They must balance a high volume
of East-West and North-South network traffic to
maximize efficiency of the data delivery.
Many of these systems must access large, high performance
database back ends.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>High availability</term>
<listitem>
<para>These types of use cases are dependent on the proper sizing
of the network to maintain replication of data between sites for
high availability. If one site becomes unavailable, the extra
sites can serve the displaced load until the original site
returns to service. It is important to size network capacity
to handle the desired loads.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Big data</term>
<listitem>
<para>Clouds used for the management and collection of big data
(data ingest) have a significant demand on network resources.
Big data often uses partial replicas of the data to maintain
integrity over large distributed clouds. Other big data
applications that require a large amount of network resources
are Hadoop, Cassandra, NuoDB, Riak, and other NoSQL and
distributed databases.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Virtual desktop infrastructure (VDI)</term>
<listitem>
<para>This use case is sensitive to network congestion, latency,
jitter, and other network characteristics. Like video streaming,
the user experience is important. However, unlike video
streaming, caching is not an option to offset the network issues.
VDI requires both upstream and downstream traffic and cannot rely
on caching for the delivery of the application to the end user.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Voice over IP (VoIP)</term>
<listitem>
<para>This is sensitive to network congestion, latency, jitter,
and other network characteristics. VoIP has a symmetrical traffic
pattern and it requires network quality of service (QoS) for best
performance. In addition, you can implement active queue management
to deliver voice and multimedia content. Users are sensitive to
latency and jitter fluctuations and can detect them at very low
levels.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Video Conference or web conference</term>
<listitem>
<para>This is sensitive to network congestion, latency, jitter,
and other network characteristics. Video Conferencing has a
symmetrical traffic pattern, but unless the network is on an
MPLS private network, it cannot use network quality of service
(QoS) to improve performance. Similar to VoIP, users are
sensitive to network performance issues even at low levels.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>High performance computing (HPC)</term>
<listitem>
<para>This is a complex use case that requires careful
consideration of the traffic flows and usage patterns to address
the needs of cloud clusters. It has high east-west traffic
patterns for distributed computing, but there can be substantial
north-south traffic depending on the specific application.</para>
</listitem>
</varlistentry>
</variablelist>
<xi:include href="network_focus/section_user_requirements_network_focus.xml"/>
<xi:include href="network_focus/section_tech_considerations_network_focus.xml"/>
<xi:include href="network_focus/section_operational_considerations_network_focus.xml"/>
<xi:include href="network_focus/section_architecture_network_focus.xml"/>
<xi:include href="network_focus/section_prescriptive_examples_network_focus.xml"/>
</chapter>

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<?xml version="1.0" encoding="UTF-8"?>
<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="arch-design-references">
<?dbhtml stop-chunking?>
<title>References</title>
<para>
<link
xlink:href="http://ec.europa.eu/justice/data-protection/">Data
Protection framework of the European Union</link>: Guidance on
Data Protection laws governed by the EU.
</para>
<para>
<link
xlink:href="http://www.internetsociety.org/deploy360/blog/2014/05/goodbye-ipv4-iana-starts-allocating-final-address-blocks/">Depletion
of IPv4 Addresses</link>: describing how IPv4 addresses and the
migration to IPv6 is inevitable.
</para>
<para>
<link
xlink:href="http://www.garrettcom.com/techsupport/papers/ethernet_switch_reliability.pdf">Ethernet
Switch Reliability</link>: ​Research white paper on Ethernet Switch
reliability.
</para>
<para>
<link
xlink:href="http://www.finra.org/Industry/Regulation/FINRARules/">Financial
Industry Regulatory Authority</link>: ​Requirements of the
Financial Industry Regulatory Authority in the USA.
</para>
<para>
<link
xlink:href="http://docs.openstack.org/cli-reference/content/chapter_cli-glance-property.html">Image
Service property keys</link>: Glance API property keys allows the
administrator to attach custom characteristics to images.
</para>
<para>
<link xlink:href="http://libguestfs.org">LibGuestFS
Documentation</link>: Official LibGuestFS documentation.
</para>
<para>
<link
xlink:href="http://docs.openstack.org/openstack-ops/content/logging_monitoring.html">Logging
and Monitoring</link>: Official OpenStack Operations
documentation.
</para>
<para>
<link xlink:href="http://manageiq.org/">ManageIQ Cloud Management
Platform</link>: An Open Source Cloud Management Platform for
managing multiple clouds.
</para>
<para>
<link
xlink:href="http://www.n-tron.com/pdf/network_availability.pdf">N-Tron
Network Availability</link>: Research white paper on network
availability.
</para>
<para>
<link
xlink:href="http://davejingtian.org/2014/03/30/nested-kvm-just-for-fun">Nested
KVM</link>: Post on how to nest KVM under KVM.
</para>
<para>
<link xlink:href="http://www.opencompute.org/">Open Compute
Project</link>: The Open Compute Project Foundation's mission is
to design and enable the delivery of the most efficient server,
storage and data center hardware designs for scalable
computing.
</para>
<para>
<link
xlink:href="http://docs.openstack.org/openstack-ops/content/flavors.html">OpenStack
Flavors</link>: Official OpenStack documentation.
</para>
<para>
<link
xlink:href="http://docs.openstack.org/ha-guide/">OpenStack
High Availability Guide</link>: Information on how to provide
redundancy for the OpenStack components.
</para>
<para>
<link
xlink:href="https://wiki.openstack.org/wiki/HypervisorSupportMatrix">OpenStack
Hypervisor Support Matrix</link>: ​Matrix of supported hypervisors
and capabilities when used with OpenStack.
</para>
<para>
<link
xlink:href="http://docs.openstack.org/developer/swift/replication_network.html">OpenStack
Object Store (Swift) Replication Reference</link>: Developer
documentation of Swift replication.
</para>
<para>
<link
xlink:href="http://docs.openstack.org/openstack-ops/">OpenStack
Operations Guide</link>: The OpenStack Operations Guide provides
information on setting up and installing OpenStack.
</para>
<para>
<link
xlink:href="http://docs.openstack.org/security-guide/">OpenStack
Security Guide</link>: The OpenStack Security Guide provides
information on securing OpenStack deployments.
</para>
<para>
<link
xlink:href="http://www.openstack.org/marketplace/training">OpenStack
Training Marketplace</link>: The OpenStack Market for training and
Vendors providing training on OpenStack.
</para>
<para>
<link
xlink:href="https://wiki.openstack.org/wiki/Pci_passthrough#How_to_check_PCI_status_with_PCI_api_paches">PCI
passthrough</link>: The PCI API patches extend the
servers/os-hypervisor to show PCI information for instance and
compute node, and also provides a resource endpoint to show PCI
information.
</para>
<para>
<link
xlink:href="https://wiki.openstack.org/wiki/TripleO">TripleO</link>:
TripleO is a program aimed at installing, upgrading and operating
OpenStack clouds using OpenStack's own cloud facilities as the
foundation.
</para>
</chapter>

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<?xml version="1.0" encoding="UTF-8"?>
<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="specialized">
<title>Specialized cases</title>
<para>Although most OpenStack architecture designs fall into one
of the seven major scenarios outlined in other sections
(compute focused, network focused, storage focused, general
purpose, multi-site, hybrid cloud, and massively scalable),
there are a few use cases that do not fit into these categories.
This section discusses these specialized cases and provide
some additional details and design considerations
for each use case:</para>
<itemizedlist>
<listitem>
<para>
<link
linkend="specialized-networking-example">Specialized
networking</link>: describes running
networking-oriented software that may involve reading
packets directly from the wire or participating in
routing protocols.
</para>
</listitem>
<listitem>
<para>
<link
linkend="software-defined-networking-sdn">Software-defined
networking (SDN)</link>: describes both
running an SDN controller from within OpenStack as well
as participating in a software-defined network.
</para>
</listitem>
<listitem>
<para>
<link
linkend="desktop-as-a-service">Desktop-as-a-Service</link>:
describes running a virtualized desktop environment
in a cloud (<glossterm>Desktop-as-a-Service</glossterm>).
This applies to private and public clouds.
</para>
</listitem>
<listitem>
<para>
<link
linkend="arch-guide-openstack-on-openstack">OpenStack on
OpenStack</link>: describes building a multi-tiered cloud by
running OpenStack on top of an OpenStack installation.
</para>
</listitem>
<listitem>
<para>
<link linkend="specialized-hardware">Specialized
hardware</link>: describes the use of specialized
hardware devices from within the OpenStack environment.
</para>
</listitem>
</itemizedlist>
<xi:include href="specialized/section_multi_hypervisor_specialized.xml"/>
<xi:include href="specialized/section_networking_specialized.xml"/>
<xi:include href="specialized/section_software_defined_networking_specialized.xml"/>
<xi:include href="specialized/section_desktop_as_a_service_specialized.xml"/>
<xi:include href="specialized/section_openstack_on_openstack_specialized.xml"/>
<xi:include href="specialized/section_hardware_specialized.xml"/>
</chapter>

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<?xml version="1.0" encoding="UTF-8"?>
<chapter xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="storage_focus">
<title>Storage focused</title>
<para>Cloud storage is a model of data storage that stores digital
data in logical pools and physical storage that spans
across multiple servers and locations. Cloud storage commonly
refers to a hosted object storage service, however the term
also includes other types of data storage that are
available as a service, for example block storage.</para>
<para>Cloud storage runs on virtualized infrastructure and
resembles broader cloud computing in terms of accessible
interfaces, elasticity, scalability, multi-tenancy, and
metered resources. You can use cloud storage services from
an off-premises service or deploy on-premises.</para>
<para>Cloud storage consists of many distributed, synonymous
resources, which are often referred to as integrated
storage clouds. Cloud storage is highly fault tolerant through
redundancy and the distribution of data. It is highly durable
through the creation of versioned copies, and can be
consistent with regard to data replicas.</para>
<para>At large scale, management of data operations is
a resource intensive process for an organization. Hierarchical
storage management (HSM) systems and data grids help
annotate and report a baseline data valuation to make
intelligent decisions and automate data decisions. HSM enables
automated tiering and movement, as well as orchestration
of data operations. A data grid is an architecture, or set of
services evolving technology, that brings together sets of
services enabling users to manage large data sets.</para>
<para>Example applications deployed with cloud
storage characteristics:</para>
<itemizedlist>
<listitem>
<para>Active archive, backups and hierarchical storage
management.</para>
</listitem>
<listitem>
<para>General content storage and synchronization. An
example of this is private dropbox.</para>
</listitem>
<listitem>
<para>Data analytics with parallel file systems.</para>
</listitem>
<listitem>
<para>Unstructured data store for services. For example,
social media back-end storage.</para>
</listitem>
<listitem>
<para>Persistent block storage.</para>
</listitem>
<listitem>
<para>Operating system and application image store.</para>
</listitem>
<listitem>
<para>Media streaming.</para>
</listitem>
<listitem>
<para>Databases.</para>
</listitem>
<listitem>
<para>Content distribution.</para>
</listitem>
<listitem>
<para>Cloud storage peering.</para>
</listitem>
</itemizedlist>
<xi:include href="storage_focus/section_tech_considerations_storage_focus.xml"/>
<xi:include href="storage_focus/section_operational_considerations_storage_focus.xml"/>
<xi:include href="storage_focus/section_architecture_storage_focus.xml"/>
<xi:include href="storage_focus/section_prescriptive_examples_storage_focus.xml"/>
</chapter>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="arch-design-architecture-hardware">
<?dbhtml stop-chunking?>
<title>Architecture</title>
<para>The hardware selection covers three areas:</para>
<itemizedlist>
<listitem>
<para>Compute</para>
</listitem>
<listitem>
<para>Network</para>
</listitem>
<listitem>
<para>Storage</para>
</listitem>
</itemizedlist>
<para>Compute-focused OpenStack clouds have high demands on processor and
memory resources, and requires hardware that can handle these demands.
Consider the following factors when selecting compute (server) hardware:</para>
<itemizedlist>
<listitem>
<para>Server density</para>
</listitem>
<listitem>
<para>Resource capacity</para>
</listitem>
<listitem>
<para>Expandability</para>
</listitem>
<listitem>
<para>Cost</para>
</listitem>
</itemizedlist>
<para>Weigh these considerations against each other to determine the
best design for the desired purpose. For example, increasing server density
means sacrificing resource capacity or expandability.</para>
<para>A compute-focused cloud should have an emphasis on server hardware
that can offer more CPU sockets, more CPU cores, and more RAM. Network
connectivity and storage capacity are less critical.</para>
<para>When designing a compute-focused OpenStack architecture, you must
consider whether you intend to scale up or scale out.
Selecting a smaller number of larger hosts, or a
larger number of smaller hosts, depends on a combination of factors:
cost, power, cooling, physical rack and floor space, support-warranty,
and manageability.</para>
<para>Considerations for selecting hardware:</para>
<itemizedlist>
<listitem>
<para>Most blade servers can support dual-socket multi-core CPUs. To
avoid this CPU limit, select <literal>full width</literal>
or <literal>full height</literal> blades.
Be aware, however, that this also decreases server density. For example,
high density blade servers such as HP BladeSystem or Dell PowerEdge
M1000e support up to 16 servers in only ten rack units. Using
half-height blades is twice as dense as using full-height blades,
which results in only eight servers per ten rack units.</para>
</listitem>
<listitem>
<para>1U rack-mounted servers that occupy only a single rack
unit may offer greater server density than a blade server
solution. It is possible to place forty 1U servers in a rack, providing
space for the top of rack (ToR) switches, compared to 32 full width
blade servers.</para>
</listitem>
<listitem>
<para>2U rack-mounted servers provide quad-socket, multi-core CPU
support, but with a corresponding decrease in server density (half
the density that 1U rack-mounted servers offer).</para>
</listitem>
<listitem>
<para>Larger rack-mounted servers, such as 4U servers, often provide
even greater CPU capacity, commonly supporting four or even eight CPU
sockets. These servers have greater expandability, but such servers
have much lower server density and are often more expensive.</para>
</listitem>
<listitem>
<para><literal>Sled servers</literal> are rack-mounted servers that
support multiple
independent servers in a single 2U or 3U enclosure. These deliver higher
density as compared to typical 1U or 2U rack-mounted servers. For
example, many sled servers offer four independent dual-socket
nodes in 2U for a total of eight CPU sockets in 2U.</para>
</listitem>
</itemizedlist>
<para>Consider these when choosing server hardware for a compute-
focused OpenStack design architecture:</para>
<itemizedlist>
<listitem>
<para>Instance density</para>
</listitem>
<listitem>
<para>Host density</para>
</listitem>
<listitem>
<para>Power and cooling density</para>
</listitem>
</itemizedlist>
<section xml:id="selecting-networking-hardware-arch">
<title>Selecting networking hardware</title>
<para>Some of the key considerations for networking hardware selection
include:</para>
<itemizedlist>
<listitem>
<para>Port count</para>
</listitem>
<listitem>
<para>Port density</para>
</listitem>
<listitem>
<para>Port speed</para>
</listitem>
<listitem>
<para>Redundancy</para>
</listitem>
<listitem>
<para>Power requirements</para>
</listitem>
</itemizedlist>
<para>We recommend designing the network architecture using
a scalable network model that makes it easy to add capacity and
bandwidth. A good example of such a model is the leaf-spline model. In
this type of network design, it is possible to easily add additional
bandwidth as well as scale out to additional racks of gear. It is
important to select network hardware that supports the required
port count, port speed, and port density while also allowing for future
growth as workload demands increase. It is also important to evaluate
where in the network architecture it is valuable to provide redundancy.</para>
</section>
<section xml:id="os-and-hypervisor-arch">
<title>Operating system and hypervisor</title>
<para>The selection of operating system (OS) and hypervisor has a
significant impact on the end point design.</para>
<para>OS and hypervisor selection impact the following areas:</para>
<itemizedlist>
<listitem>
<para>Cost</para>
</listitem>
<listitem>
<para>Supportability</para>
</listitem>
<listitem>
<para>Management tools</para>
</listitem>
<listitem>
<para>Scale and performance</para>
</listitem>
<listitem>
<para>Security</para>
</listitem>
<listitem>
<para>Supported features</para>
</listitem>
<listitem>
<para>Interoperability</para>
</listitem>
</itemizedlist>
</section>
<section xml:id="openstack-components-arch">
<title>OpenStack components</title>
<para>The selection of OpenStack components is important.
There are certain components that are required, for example the compute
and image services, but others, such as the Orchestration service, may not
be present.</para>
<para>For a compute-focused OpenStack design architecture, the
following components may be present:</para>
<itemizedlist>
<listitem>
<para>Identity (keystone)</para>
</listitem>
<listitem>
<para>Dashboard (horizon)</para>
</listitem>
<listitem>
<para>Compute (nova)</para>
</listitem>
<listitem>
<para>Object Storage (swift)</para>
</listitem>
<listitem>
<para>Image (glance)</para>
</listitem>
<listitem>
<para>Networking (neutron)</para>
</listitem>
<listitem>
<para>Orchestration (heat)</para>
</listitem>
</itemizedlist>
<note>
<para>A compute-focused design is less likely to include OpenStack Block
Storage. However, there may be some situations where the need for
performance requires a block storage component to improve data I-O.</para>
</note>
<para>The exclusion of certain OpenStack components might also limit the
functionality of other components. If a design includes
the Orchestration service but excludes the Telemetry service, then
the design cannot take advantage of Orchestration's auto
scaling functionality as this relies on information from Telemetry.</para>
</section>
<section xml:id="networking-software-arch">
<title>Networking software</title>
<para>OpenStack Networking provides a wide variety of networking services
for instances. There are many additional networking software packages
that might be useful to manage the OpenStack components themselves.
The <citetitle>OpenStack High Availability Guide</citetitle>
(<link xlink:href="http://docs.openstack.org/ha-guide/">http://docs.openstack.org/ha-guide/</link>)
describes some of these software packages in more detail.
</para>
<para>For a compute-focused OpenStack cloud, the OpenStack infrastructure
components must be highly available. If the design does not
include hardware load balancing, you must add networking software packages,
for example, HAProxy.</para>
</section>
<section xml:id="management-software-arch">
<title>Management software</title>
<para>The selected supplemental software solution impacts and affects
the overall OpenStack cloud design. This includes software for
providing clustering, logging, monitoring and alerting.</para>
<para>The availability of design requirements is the main determiner
for the inclusion of clustering software, such as Corosync or Pacemaker.</para>
<para>Operational considerations determine the requirements for logging,
monitoring, and alerting. Each of these sub-categories include
various options.</para>
<para>Some other potential design impacts include:</para>
<variablelist>
<varlistentry>
<term>OS-hypervisor combination</term>
<listitem>
<para>Ensure that the selected logging,
monitoring, or alerting tools support the proposed OS-hypervisor
combination.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Network hardware</term>
<listitem>
<para>The logging, monitoring, and alerting software
must support the network hardware selection.</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="database-software-arch">
<title>Database software</title>
<para>A large majority of OpenStack components require access to
back-end database services to store state and configuration
information. Select an appropriate back-end database that
satisfies the availability and fault tolerance requirements of the
OpenStack services. OpenStack services support connecting
to any database that the SQLAlchemy Python drivers support,
however most common database deployments make use of MySQL or some
variation of it. We recommend that you make the database that provides
back-end services within a general-purpose cloud highly
available. Some of the more common software solutions include Galera,
MariaDB, and MySQL with multi-master replication.</para>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="operational-considerations-compute-focus">
<?dbhtml stop-chunking?>
<title>Operational considerations</title>
<para>There are a number of operational considerations that affect the
design of compute-focused OpenStack clouds, including:</para>
<itemizedlist>
<listitem>
<para>
Enforcing strict API availability requirements
</para>
</listitem>
<listitem>
<para>
Understanding and dealing with failure scenarios
</para>
</listitem>
<listitem>
<para>
Managing host maintenance schedules
</para>
</listitem>
</itemizedlist>
<para>Service-level agreements (SLAs) are contractual obligations that
ensure the availability of a service. When designing an OpenStack cloud,
factoring in promises of availability implies a certain level of
redundancy and resiliency.</para>
<section xml:id="montioring-compute-focus">
<title>Monitoring</title>
<para>OpenStack clouds require appropriate monitoring platforms
to catch and manage errors.</para>
<note>
<para>We recommend leveraging existing monitoring systems
to see if they are able to effectively monitor an
OpenStack environment.</para>
</note>
<para>Specific meters that are critically important to capture
include:</para>
<itemizedlist>
<listitem>
<para>Image disk utilization</para>
</listitem>
<listitem>
<para>Response time to the Compute API</para>
</listitem>
</itemizedlist>
</section>
<section xml:id="capacity-planning-operational">
<title>Capacity planning</title>
<para>Adding extra capacity to an OpenStack cloud is a
horizontally scaling process.</para>
<para>We recommend similar (or the same) CPUs
when adding extra nodes to the environment. This reduces
the chance of breaking live-migration features if they are
present. Scaling out hypervisor hosts also has a direct effect
on network and other data center resources. We recommend you
factor in this increase when reaching rack capacity or when requiring
extra network switches.</para>
<para>Changing the internal components of a Compute host to account for
increases in demand is a process known as vertical scaling.
Swapping a CPU for one with more cores, or
increasing the memory in a server, can help add extra
capacity for running applications.</para>
<para>Another option is to assess the average workloads and
increase the number of instances that can run within the
compute environment by adjusting the overcommit ratio.</para>
<note>
<para>It is important to remember that changing the CPU
overcommit ratio can have a detrimental effect and cause
a potential increase in a noisy neighbor.</para>
</note>
<para>The added risk of increasing the overcommit ratio is that
more instances fail when a compute host fails. We do not recommend
that you increase the CPU overcommit ratio in compute-focused
OpenStack design architecture, as it can increase the potential
for noisy neighbor issues.</para>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="prescriptive-example-compute-focus">
<?dbhtml stop-chunking?>
<title>Prescriptive examples</title>
<para>The Conseil Européen pour la Recherche Nucléaire (CERN),
also known as the European Organization for Nuclear Research,
provides particle accelerators and other infrastructure for
high-energy physics research.</para>
<para>As of 2011 CERN operated these two compute centers in Europe
with plans to add a third.</para>
<informaltable rules="all">
<col width="40%" />
<col width="60%" />
<thead>
<tr><th>Data center</th><th>Approximate capacity</th></tr>
</thead>
<tbody>
<tr>
<td>Geneva, Switzerland</td>
<td>
<itemizedlist>
<listitem><para>3.5 Mega Watts</para></listitem>
<listitem><para>91000 cores</para></listitem>
<listitem><para>120 PB HDD</para></listitem>
<listitem><para>100 PB Tape</para></listitem>
<listitem><para>310 TB Memory</para></listitem>
</itemizedlist>
</td>
</tr>
<tr>
<td>Budapest, Hungary</td>
<td>
<itemizedlist>
<listitem><para>2.5 Mega Watts</para></listitem>
<listitem><para>20000 cores</para></listitem>
<listitem><para>6 PB HDD</para></listitem>
</itemizedlist>
</td>
</tr>
</tbody>
</informaltable>
<para>To support a growing number of compute-heavy users of
experiments related to the Large Hadron Collider (LHC), CERN
ultimately elected to deploy an OpenStack cloud using
Scientific Linux and RDO. This effort aimed to simplify the
management of the center's compute resources with a view to
doubling compute capacity through the addition of a
data center in 2013 while maintaining the same
levels of compute staff.</para>
<para>The CERN solution uses <glossterm baseform="cell">cells</glossterm>
for segregation of compute
resources and for transparently scaling between different data
centers. This decision meant trading off support for security
groups and live migration. In addition, they must manually replicate
some details, like flavors, across cells. In
spite of these drawbacks cells provide the
required scale while exposing a single public API endpoint to
users.</para>
<para>CERN created a compute cell for each of the two original data
centers and created a third when it added a new data center
in 2013. Each cell contains three availability zones to
further segregate compute resources and at least three
RabbitMQ message brokers configured for clustering with
mirrored queues for high availability.</para>
<para>The API cell, which resides behind a HAProxy load balancer,
is in the data center in Switzerland and directs API
calls to compute cells using a customized variation of the
cell scheduler. The customizations allow certain workloads to
route to a specific data center or all data centers,
with cell RAM availability determining cell selection in the
latter case.</para>
<mediaobject>
<imageobject>
<imagedata contentwidth="4in" fileref="../figures/Generic_CERN_Example.png"/>
</imageobject>
</mediaobject>
<para>There is also some customization of the filter scheduler
that handles placement within the cells:</para>
<variablelist>
<varlistentry><term>ImagePropertiesFilter</term>
<listitem>
<para>Provides special handling
depending on the guest operating system in use
(Linux-based or Windows-based).</para>
</listitem>
</varlistentry>
<varlistentry><term>ProjectsToAggregateFilter</term>
<listitem><para>Provides special
handling depending on which project the instance is
associated with.</para>
</listitem>
</varlistentry>
<varlistentry><term>default_schedule_zones</term>
<listitem><para>Allows the selection of
multiple default availability zones, rather than a
single default.</para>
</listitem>
</varlistentry>
</variablelist>
<para>A central database team manages the MySQL database server in each cell
in an active/passive configuration with a NetApp storage back end.
Backups run every 6 hours.</para>
<section xml:id="network-architecture">
<title>Network architecture</title>
<para>To integrate with existing networking infrastructure, CERN
made customizations to legacy networking (nova-network). This was in the
form of a driver to integrate with CERN's existing database
for tracking MAC and IP address assignments.</para>
<para>The driver facilitates selection of a MAC address and IP for
new instances based on the compute node where the scheduler places
the instance.</para>
<para>The driver considers the compute node where the scheduler
placed an instance and selects a MAC address and IP
from the pre-registered list associated with that node in the
database. The database updates to reflect the address assignment to
that instance.</para>
</section>
<section xml:id="storage-architecture">
<title>Storage architecture</title>
<para>CERN deploys the OpenStack Image service in the API cell and
configures it to expose version 1 (V1) of the API. This also requires
the image registry. The storage back end in
use is a 3 PB Ceph cluster.</para>
<para>CERN maintains a small set of Scientific Linux 5 and 6 images onto
which orchestration tools can place applications. Puppet manages
instance configuration and customization.</para>
</section>
<section xml:id="monitoring">
<title>Monitoring</title>
<para>CERN does not require direct billing, but uses the Telemetry service
to perform metering for the purposes of adjusting
project quotas. CERN uses a sharded, replicated, MongoDB back-end.
To spread API load, CERN deploys instances of the nova-api service
within the child cells for Telemetry to query
against. This also requires the configuration of supporting services
such as keystone, glance-api, and glance-registry in the child cells.
</para>
<mediaobject>
<imageobject>
<imagedata contentwidth="4in"
fileref="../figures/Generic_CERN_Architecture.png"/>
</imageobject>
</mediaobject>
<para>
Additional monitoring tools in use include <link
xlink:href="http://flume.apache.org/">Flume</link>, <link
xlink:href="http://www.elasticsearch.org/">Elastic
Search</link>, <link
xlink:href="http://www.elasticsearch.org/overview/kibana/">Kibana</link>,
and the CERN developed <link
xlink:href="http://lemon.web.cern.ch/lemon/index.shtml">Lemon</link>
project.
</para>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE section [
<!ENTITY % openstack SYSTEM "../../common/entities/openstack.ent">
%openstack;
]>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="technical-considerations-compute-focus">
<?dbhtml stop-chunking?>
<title>Technical considerations</title>
<para>In a compute-focused OpenStack cloud, the type of instance
workloads you provision heavily influences technical
decision making.</para>
<para>Public and private clouds require deterministic capacity
planning to support elastic growth in order to meet user SLA
expectations. Deterministic capacity planning is the path to
predicting the effort and expense of making a given process
perform consistently. This process is important because,
when a service becomes a critical part of a user's
infrastructure, the user's experience links directly to the SLAs of
the cloud itself.</para>
<para>There are two aspects of capacity planning to consider:</para>
<itemizedlist>
<listitem>
<para>Planning the initial deployment footprint</para>
</listitem>
<listitem>
<para>Planning expansion of the environment to stay ahead of the
demands of cloud users</para>
</listitem>
</itemizedlist>
<para>Begin planning an initial OpenStack deployment footprint with
estimations of expected uptake, and existing infrastructure workloads.</para>
<para>The starting point is the core count of the cloud. By
applying relevant ratios, the user can gather information
about:</para>
<itemizedlist>
<listitem>
<para>The number of expected concurrent instances:
(overcommit fraction × cores) / virtual cores per instance</para>
</listitem>
<listitem>
<para>Required storage: flavor disk size × number of instances</para>
</listitem>
</itemizedlist>
<para>These ratios determine the amount of
additional infrastructure needed to support the cloud. For
example, consider a situation in which you require 1600
instances, each with 2 vCPU and 50 GB of storage. Assuming the
default overcommit rate of 16:1, working out the math provides
an equation of:</para>
<itemizedlist>
<listitem>
<para>1600 = (16 &times; (number of physical cores)) / 2</para>
</listitem>
<listitem>
<para>Storage required = 50&nbsp;GB &times; 1600</para>
</listitem>
</itemizedlist>
<para>On the surface, the equations reveal the need for 200
physical cores and 80&nbsp;TB of storage for
<filename>/var/lib/nova/instances/</filename>. However,
it is also important to
look at patterns of usage to estimate the load that the API
services, database servers, and queue servers are likely to
encounter.</para>
<para>Aside from the creation and termination of instances, consider the
impact of users accessing the service,
particularly on nova-api and its associated database. Listing
instances gathers a great deal of information and given the
frequency with which users run this operation, a cloud with a
large number of users can increase the load significantly.
This can even occur unintentionally. For example, the
OpenStack Dashboard instances tab refreshes the list of
instances every 30 seconds, so leaving it open in a browser
window can cause unexpected load.</para>
<para>Consideration of these factors can help determine how many
cloud controller cores you require. A server with 8 CPU cores
and 8 GB of RAM server would be sufficient for a rack of
compute nodes, given the above caveats.</para>
<para>Key hardware specifications are also crucial to the
performance of user instances. Be sure to consider budget and
performance needs, including storage performance
(spindles/core), memory availability (RAM/core), network
bandwidth (Gbps/core), and overall CPU performance
(CPU/core).</para>
<para>The cloud resource calculator is a useful tool in examining
the impacts of different hardware and instance load outs. See:
<link xlink:href="https://github.com/noslzzp/cloud-resource-calculator/blob/master/cloud-resource-calculator.ods">https://github.com/noslzzp/cloud-resource-calculator/blob/master/cloud-resource-calculator.ods</link>
</para>
<section xml:id="expansion-planning-compute-focus">
<title>Expansion planning</title>
<para>A key challenge for planning the expansion of cloud
compute services is the elastic nature of cloud infrastructure
demands.</para>
<para>Planning for expansion is a balancing act.
Planning too conservatively can lead to unexpected
oversubscription of the cloud and dissatisfied users. Planning
for cloud expansion too aggressively can lead to unexpected
underutilization of the cloud and funds spent unnecessarily on operating
infrastructure.</para>
<para>The key is to carefully monitor the trends in
cloud usage over time. The intent is to measure the
consistency with which you deliver services, not the
average speed or capacity of the cloud. Using this information
to model capacity performance enables users to more
accurately determine the current and future capacity of the
cloud.</para>
</section>
<section xml:id="cpu-and-ram-compute-focus">
<title>CPU and RAM</title>
<para>OpenStack enables users to overcommit CPU and RAM on
compute nodes. This allows an increase in the number of
instances running on the cloud at the cost of reducing the
performance of the instances. OpenStack Compute uses the
following ratios by default:</para>
<itemizedlist>
<listitem>
<para>CPU allocation ratio: 16:1</para>
</listitem>
<listitem>
<para>RAM allocation ratio: 1.5:1</para>
</listitem>
</itemizedlist>
<para>The default CPU allocation ratio of 16:1 means that the
scheduler allocates up to 16 virtual cores per physical core.
For example, if a physical node has 12 cores, the scheduler
sees 192 available virtual cores. With typical flavor
definitions of 4 virtual cores per instance, this ratio would
provide 48 instances on a physical node.</para>
<para>Similarly, the default RAM allocation ratio of 1.5:1 means
that the scheduler allocates instances to a physical node as
long as the total amount of RAM associated with the instances
is less than 1.5 times the amount of RAM available on the
physical node.</para>
<para>You must select the appropriate CPU and RAM allocation ratio
based on particular use cases.</para>
</section>
<section xml:id="additional-hardware-compute-focus">
<title>Additional hardware</title>
<para>Certain use cases may benefit from exposure to additional
devices on the compute node. Examples might include:</para>
<itemizedlist>
<listitem>
<para>High performance computing jobs that benefit from
the availability of graphics processing units (GPUs)
for general-purpose computing.</para>
</listitem>
<listitem>
<para>Cryptographic routines that benefit from the
availability of hardware random number generators to
avoid entropy starvation.</para>
</listitem>
<listitem>
<para>Database management systems that benefit from the
availability of SSDs for ephemeral storage to maximize
read/write time.</para>
</listitem>
</itemizedlist>
<para>Host aggregates group hosts that share similar
characteristics, which can include hardware similarities. The
addition of specialized hardware to a cloud deployment is
likely to add to the cost of each node, so consider carefully
whether all compute nodes, or
just a subset targeted by flavors, need the
additional customization to support the desired
workloads.</para>
</section>
<section xml:id="utilization">
<title>Utilization</title>
<para>Infrastructure-as-a-Service offerings, including OpenStack,
use flavors to provide standardized views of virtual machine
resource requirements that simplify the problem of scheduling
instances while making the best use of the available physical
resources.</para>
<para>In order to facilitate packing of virtual machines onto
physical hosts, the default selection of flavors provides a
second largest flavor that is half the size
of the largest flavor in every dimension. It has half the
vCPUs, half the vRAM, and half the ephemeral disk space. The
next largest flavor is half that size again. The following figure
provides a visual representation of this concept for a general
purpose computing design:
<mediaobject>
<imageobject>
<imagedata contentwidth="4in"
fileref="../figures/Compute_Tech_Bin_Packing_General1.png"
/>
</imageobject>
</mediaobject></para>
<para>The following figure displays a CPU-optimized, packed server:
<mediaobject>
<imageobject>
<imagedata contentwidth="4in"
fileref="../figures/Compute_Tech_Bin_Packing_CPU_optimized1.png"
/>
</imageobject>
</mediaobject></para>
<para>These default flavors are well suited to typical configurations
of commodity server hardware. To maximize utilization,
however, it may be necessary to customize the flavors or
create new ones in order to better align instance sizes to the
available hardware.</para>
<para>Workload characteristics may also influence hardware choices
and flavor configuration, particularly where they present
different ratios of CPU versus RAM versus HDD
requirements.</para>
<para>For more information on Flavors see:
<link xlink:href="http://docs.openstack.org/openstack-ops/content/flavors.html">OpenStack Operations Guide: Flavors</link></para>
</section>
<section xml:id="openstack-components-compute-focus">
<title>OpenStack components</title>
<para>Due to the nature of the workloads in this
scenario, a number of components are highly beneficial for
a Compute-focused cloud. This includes the typical OpenStack
components:</para>
<itemizedlist>
<listitem>
<para>OpenStack Compute (nova)</para>
</listitem>
<listitem>
<para>OpenStack Image service (glance)</para>
</listitem>
<listitem>
<para>OpenStack Identity (keystone)</para>
</listitem>
</itemizedlist>
<para>Also consider several specialized components:</para>
<itemizedlist>
<listitem>
<para><glossterm>Orchestration</glossterm> (heat)</para>
<para>Given the nature of the
applications involved in this scenario, these are heavily
automated deployments. Making use of Orchestration is highly
beneficial in this case. You can script the deployment of a
batch of instances and the running of tests, but it
makes sense to use the Orchestration service
to handle all these actions.</para>
</listitem>
<listitem>
<para>Telemetry (ceilometer)</para>
<para>Telemetry and the alarms it generates support autoscaling
of instances using Orchestration. Users that are not using the
Orchestration service do not need to deploy the Telemetry
service and may choose to use external solutions to fulfill
their metering and monitoring requirements.</para>
</listitem>
<listitem>
<para>OpenStack Block Storage (cinder)</para>
<para>Due to the burst-able nature of the workloads and the
applications and instances that perform batch
processing, this cloud mainly uses memory or CPU, so
the need for add-on storage to each instance is not a likely
requirement. This does not mean that you do not use
OpenStack Block Storage (cinder) in the infrastructure, but
typically it is not a central component.</para>
</listitem>
<listitem>
<para>Networking</para>
<para>When choosing a networking platform, ensure that it either
works with all desired hypervisor and container technologies
and their OpenStack drivers, or that it includes an implementation of
an ML2 mechanism driver. You can mix networking platforms
that provide ML2 mechanisms drivers.</para>
</listitem>
</itemizedlist>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE section [
<!ENTITY % openstack SYSTEM "../../common/entities/openstack.ent">
%openstack;
]>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="arch-guide-architecture-overview">
<?dbhtml stop-chunking?>
<title>Architecture</title>
<para>Hardware selection involves three key areas:</para>
<itemizedlist>
<listitem>
<para>Compute</para>
</listitem>
<listitem>
<para>Network</para>
</listitem>
<listitem>
<para>Storage</para>
</listitem>
</itemizedlist>
<para>Hardware for a general purpose OpenStack cloud
should reflect a cloud with no pre-defined usage model,
designed to run a wide variety of applications with
varying resource usage requirements.
These applications include any of the following:</para>
<itemizedlist>
<listitem>
<para>
RAM-intensive
</para>
</listitem>
<listitem>
<para>
CPU-intensive
</para>
</listitem>
<listitem>
<para>
Storage-intensive
</para>
</listitem>
</itemizedlist>
<para>Certain hardware form factors may better suit a general
purpose OpenStack cloud due to the requirement for equal (or
nearly equal) balance of resources. Server hardware must provide
the following:</para>
<itemizedlist>
<listitem>
<para>
Equal (or nearly equal) balance of compute capacity (RAM and CPU)
</para>
</listitem>
<listitem>
<para>
Network capacity (number and speed of links)
</para>
</listitem>
<listitem>
<para>
Storage capacity (gigabytes or terabytes as well as Input/Output
Operations Per Second (<glossterm>IOPS</glossterm>)
</para>
</listitem>
</itemizedlist>
<para>Evaluate server hardware around four conflicting
dimensions:</para>
<variablelist>
<varlistentry>
<term>Server density</term>
<listitem>
<para>A measure of how many servers can
fit into a given measure of physical space, such as a
rack unit [U].</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Resource capacity</term>
<listitem>
<para>The number of CPU cores, amount of RAM,
or amount of deliverable storage.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Expandability</term>
<listitem>
<para>Limit of additional resources you can add to
a server.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Cost</term>
<listitem>
<para>The relative purchase price of the hardware
weighted against the level of design effort needed to
build the system.</para>
</listitem>
</varlistentry>
</variablelist>
<para>Increasing server density means sacrificing resource
capacity or expandability, however, increasing resource
capacity and expandability increases cost and decreases server
density. As a result, determining the best server hardware for
a general purpose OpenStack architecture means understanding
how choice of form factor will impact the rest of the
design. The following list outlines the form factors to
choose from:</para>
<itemizedlist>
<listitem>
<para>Blade servers typically support dual-socket
multi-core CPUs. Blades also offer
outstanding density.</para>
</listitem>
<listitem>
<para>1U rack-mounted servers occupy only a single rack
unit. Their benefits include high density, support for
dual-socket multi-core CPUs, and support for
reasonable RAM amounts. This form factor offers
limited storage capacity, limited network capacity,
and limited expandability.</para>
</listitem>
<listitem>
<para>2U rack-mounted servers offer the expanded storage
and networking capacity that 1U servers tend to lack,
but with a corresponding decrease in server density
(half the density offered by 1U rack-mounted
servers).</para>
</listitem>
<listitem>
<para>Larger rack-mounted servers, such as 4U servers,
will tend to offer even greater CPU capacity, often
supporting four or even eight CPU sockets. These
servers often have much greater expandability so will
provide the best option for upgradability. This means,
however, that the servers have a much lower server
density and a much greater hardware cost.</para>
</listitem>
<listitem>
<para><emphasis>Sled servers</emphasis> are rack-mounted servers that support
multiple independent servers in a single 2U or 3U
enclosure. This form factor offers increased density
over typical 1U-2U rack-mounted servers but tends to
suffer from limitations in the amount of storage or
network capacity each individual server
supports.</para>
</listitem>
</itemizedlist>
<para>The best form factor for server hardware
supporting a general purpose OpenStack cloud is driven by
outside business and cost factors. No single reference
architecture applies to all implementations; the decision
must flow from user requirements, technical
considerations, and operational considerations. Here are some
of the key factors that influence the selection of server
hardware:</para>
<variablelist>
<varlistentry>
<term>Instance density</term>
<listitem>
<para>Sizing is an important
consideration for a general purpose OpenStack cloud.
The expected or anticipated number of instances that
each hypervisor can host is a common meter used in
sizing the deployment. The selected server hardware
needs to support the expected or anticipated instance
density.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Host density</term>
<listitem>
<para>Physical data centers have limited
physical space, power, and cooling. The number of
hosts (or hypervisors) that can be fitted into a given
metric (rack, rack unit, or floor tile) is another
important method of sizing. Floor weight is an often
overlooked consideration. The data center floor must
be able to support the weight of the proposed number
of hosts within a rack or set of racks. These factors
need to be applied as part of the host density
calculation and server hardware selection.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Power density</term>
<listitem>
<para>Data centers have a specified amount
of power fed to a given rack or set of racks. Older
data centers may have a power density as power as low
as 20 AMPs per rack, while more recent data centers
can be architected to support power densities as high
as 120 AMP per rack. The selected server hardware must
take power density into account.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Network connectivity</term>
<listitem>
<para>The selected server hardware
must have the appropriate number of network
connections, as well as the right type of network
connections, in order to support the proposed
architecture. Ensure that, at a minimum, there are at
least two diverse network connections coming into each
rack.</para>
</listitem>
</varlistentry>
</variablelist>
<para>The selection of form factors or architectures affects the selection
of server hardware. Ensure that the selected server hardware
is configured to support enough storage capacity (or storage
expandability) to match the requirements of selected scale-out
storage solution. Similarly, the network architecture impacts
the server hardware selection and vice versa.</para>
<section xml:id="selecting-storage-hardware">
<title>Selecting storage hardware</title>
<para>Determine storage hardware architecture by
selecting specific storage architecture. Determine the selection of
storage architecture by evaluating possible solutions against the
critical factors, the user requirements, technical
considerations, and operational considerations.
Incorporate the following facts into your storage architecture:</para>
<variablelist>
<varlistentry>
<term>Cost</term>
<listitem>
<para>Storage can be a significant portion of the
overall system cost. For an organization that is concerned
with vendor support, a commercial storage solution is
advisable, although it comes with a higher price
tag. If initial capital expenditure requires
minimization, designing a system based on commodity
hardware would apply. The trade-off is potentially
higher support costs and a greater risk of
incompatibility and interoperability issues.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Scalability</term>
<listitem>
<para>Scalability, along with expandability, is a major
consideration in a general purpose OpenStack cloud. It
might be difficult to predict the final intended size
of the implementation as there are no established
usage patterns for a general purpose cloud. It might
become necessary to expand the initial deployment in
order to accommodate growth and user demand.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Expandability</term>
<listitem>
<para>Expandability is a major architecture factor for
storage solutions with general purpose OpenStack
cloud. A storage solution that expands
to 50&nbsp;PB is considered more expandable than a
solution that only scales to 10&nbsp;PB. This meter
is related to scalability, which is the measure of a
solution's performance as it expands.</para>
</listitem>
</varlistentry>
</variablelist>
<para>Using a scale-out storage solution with direct-attached
storage (DAS) in the servers is well suited for a general
purpose OpenStack cloud. Cloud services requirements determine
your choice of scale-out solution. You need to determine if
a single, highly expandable and highly vertical, scalable,
centralized storage array is suitable for your design.
After determining an approach, select the storage hardware
based on this criteria.</para>
<para>This list expands upon the potential impacts for including a
particular storage architecture (and corresponding storage
hardware) into the design for a general purpose OpenStack
cloud:</para>
<variablelist>
<varlistentry>
<term>Connectivity</term>
<listitem>
<para>Ensure that, if storage protocols
other than Ethernet are part of the storage solution,
the appropriate hardware has been selected.
If a centralized storage array is selected, ensure
that the hypervisor will be able to connect to that
storage array for image storage.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Usage</term>
<listitem>
<para>How the particular storage architecture will
be used is critical for determining the architecture.
Some of the configurations that will influence the
architecture include whether it will be used by the
hypervisors for ephemeral instance storage or if
OpenStack Object Storage will use it for object storage.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Instance and image locations</term>
<listitem>
<para>
Where instances and images will be stored will influence
the architecture.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Server hardware</term>
<listitem>
<para>If the solution is a scale-out
storage architecture that includes DAS, it
will affect the server hardware selection. This could
ripple into the decisions that affect host density,
instance density, power density, OS-hypervisor,
management tools and others.</para>
</listitem>
</varlistentry>
</variablelist>
<para>General purpose OpenStack cloud has multiple options.
The key factors that will have an influence
on selection of storage hardware for a general purpose
OpenStack cloud are as follows:</para>
<variablelist>
<varlistentry>
<term>Capacity</term>
<listitem>
<para>Hardware resources selected for the resource nodes
should be capable of supporting enough storage for the
cloud services. Defining the initial requirements and
ensuring the design can support adding capacity is
important. Hardware nodes selected for object storage
should be capable of support a large number of inexpensive
disks with no reliance on RAID controller cards.
Hardware nodes selected for block storage should be capable
of supporting high speed storage solutions and RAID controller
cards to provide performance and redundancy to storage at a
hardware level.
Selecting hardware RAID controllers that automatically repair
damaged arrays will assist with the replacement and repair of
degraded or deleted storage devices.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Performance</term>
<listitem>
<para>Disks selected for object storage services do not need
to be fast performing disks. We recommend that object storage
nodes take advantage of the best cost per terabyte available
for storage. Contrastingly, disks chosen for block storage
services should take advantage of performance boosting
features that may entail the use of SSDs or flash storage
to provide high performance block storage pools. Storage
performance of ephemeral disks used for instances should
also be taken into consideration.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Fault tolerance</term>
<listitem>
<para>Object storage resource nodes have
no requirements for hardware fault tolerance or RAID
controllers. It is not necessary to plan for fault
tolerance within the object storage hardware because
the object storage service provides replication
between zones as a feature of the service. Block
storage nodes, compute nodes, and cloud controllers
should all have fault tolerance built in at the
hardware level by making use of hardware RAID
controllers and varying levels of RAID configuration.
The level of RAID chosen should be consistent with the
performance and availability requirements of the
cloud.</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="selecting-networking-hardware">
<title>Selecting networking hardware</title>
<para>Selecting network architecture determines which network
hardware will be used. Networking software is determined by
the selected networking hardware.</para>
<para>There are more subtle design impacts that need to be considered.
The selection of certain networking hardware (and the networking software)
affects the management tools that can be used. There are
exceptions to this; the rise of <emphasis>open</emphasis> networking software
that supports a range of networking hardware means that there
are instances where the relationship between networking
hardware and networking software are not as tightly defined.</para>
<para>Some of the key considerations that should be included in
the selection of networking hardware include:</para>
<variablelist>
<varlistentry>
<term>Port count</term>
<listitem>
<para>The design will require networking
hardware that has the requisite port count.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Port density</term>
<listitem>
<para>The network design will be affected by
the physical space that is required to provide the
requisite port count. A higher port density is preferred,
as it leaves more rack space for compute or storage components
that may be required by the design. This can also lead into
concerns about fault domains and power density that
should be considered. Higher density switches are more
expensive and should also be considered, as it is
important not to over design the network if it is not
required.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Port speed</term>
<listitem>
<para>
The networking hardware must support the proposed
network speed, for example: 1&nbsp;GbE, 10&nbsp;GbE, or
40&nbsp;GbE (or even 100&nbsp;GbE).</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Redundancy</term>
<listitem>
<para>The level of network hardware redundancy
required is influenced by the user requirements for
high availability and cost considerations. Network
redundancy can be achieved by adding redundant power
supplies or paired switches. If this is a requirement,
the hardware will need to support this configuration.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Power requirements</term>
<listitem>
<para>Ensure that the physical data
center provides the necessary power for the selected
network hardware.</para>
<note>
<para>
This may be an issue for spine switches in a leaf and
spine fabric, or end of row (EoR) switches.</para>
</note>
</listitem>
</varlistentry>
</variablelist>
<para>There is no single best practice architecture for the
networking hardware supporting a general purpose OpenStack
cloud that will apply to all implementations. Some of the key
factors that will have a strong influence on selection of
networking hardware include:</para>
<variablelist>
<varlistentry>
<term>Connectivity</term>
<listitem>
<para>All nodes within an OpenStack cloud
require network connectivity. In some
cases, nodes require access to more than one network
segment. The design must encompass sufficient network
capacity and bandwidth to ensure that all
communications within the cloud, both north-south and
east-west traffic have sufficient resources
available.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Scalability</term>
<listitem>
<para>The network design should
encompass a physical and logical network design that
can be easily expanded upon. Network hardware should
offer the appropriate types of interfaces and speeds
that are required by the hardware nodes.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Availability</term>
<listitem>
<para>To ensure that access to nodes within
the cloud is not interrupted, we recommend that
the network architecture identify any single points of
failure and provide some level of redundancy or fault
tolerance. With regard to the network infrastructure
itself, this often involves use of networking
protocols such as LACP, VRRP or others to achieve a
highly available network connection. In addition, it
is important to consider the networking implications
on API availability. In order to ensure that the APIs,
and potentially other services in the cloud are highly
available, we recommend you design a load balancing
solution within the network architecture to
accommodate for these requirements.</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="software-selection">
<title>Software selection</title>
<para>Software selection for a general purpose OpenStack
architecture design needs to include these three areas:</para>
<itemizedlist>
<listitem>
<para>Operating system (OS) and hypervisor</para>
</listitem>
<listitem>
<para>OpenStack components</para>
</listitem>
<listitem>
<para>Supplemental software</para>
</listitem>
</itemizedlist>
</section>
<section xml:id="os-and-hypervisor">
<title>Operating system and hypervisor</title>
<para>The operating system (OS) and hypervisor have a
significant impact on the overall design. Selecting a particular
operating system and hypervisor can directly affect server
hardware selection. Make sure the storage
hardware and topology support the selected operating
system and hypervisor combination. Also ensure the networking
hardware selection and topology will work with the chosen operating
system and hypervisor combination.</para>
<para>Some areas that could be impacted by the selection of OS and
hypervisor include:</para>
<variablelist>
<varlistentry>
<term>Cost</term>
<listitem>
<para>Selecting a commercially supported hypervisor,
such as Microsoft Hyper-V, will result in a different
cost model rather than community-supported open source
hypervisors including <glossterm
baseform="kernel-based VM (KVM)">KVM</glossterm>,
Kinstance or <glossterm>Xen</glossterm>. When
comparing open source OS solutions, choosing Ubuntu
over Red Hat (or vice versa) will have an impact on
cost due to support contracts.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Supportability</term>
<listitem>
<para>Depending on the selected
hypervisor, staff should have the appropriate
training and knowledge to support the selected OS and
hypervisor combination. If they do not, training will
need to be provided which could have a cost impact on
the design.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Management tools</term>
<listitem>
<para>The management tools used for
Ubuntu and Kinstance differ from the management tools
for VMware vSphere. Although both OS and hypervisor
combinations are supported by OpenStack, there will be
very different impacts to the rest of the design as a
result of the selection of one combination versus the
other.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Scale and performance</term>
<listitem>
<para>Ensure that selected OS and
hypervisor combinations meet the appropriate scale and
performance requirements. The chosen architecture will
need to meet the targeted instance-host ratios with
the selected OS-hypervisor combinations.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Security</term>
<listitem>
<para>Ensure that the design can accommodate
regular periodic installations of application security
patches while maintaining required workloads. The
frequency of security patches for the proposed
OS-hypervisor combination will have an impact on
performance and the patch installation process could
affect maintenance windows.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Supported features</term>
<listitem>
<para>Determine which features of OpenStack are required.
This will often determine the selection of the OS-hypervisor combination.
Some features are only available with specific operating systems or
hypervisors.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Interoperability</term>
<listitem>
<para>You will need to consider how the OS and hypervisor combination
interactions with other operating systems and hypervisors, including
other software solutions.
Operational troubleshooting tools for one OS-hypervisor
combination may differ from the tools used for another OS-hypervisor
combination and, as a result, the design will need to
address if the two sets of tools need to interoperate.</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="openstack-components">
<title>OpenStack components</title>
<para>Selecting which OpenStack components are included in the overall
design is important. Some OpenStack components, like
compute and Image service, are required in every architecture. Other
components, like Orchestration, are not always required.</para>
<para>Excluding certain OpenStack components can limit or constrain
the functionality of other components. For example, if the architecture includes
Orchestration but excludes Telemetry, then the design will not be able
to take advantage of Orchestrations' auto scaling functionality.
It is important to research the component interdependencies
in conjunction with the technical requirements before deciding
on the final architecture.</para>
<section xml:id="networking-software">
<title>Networking software</title>
<para>OpenStack Networking (neutron) provides a wide variety of networking
services for instances. There are many additional networking
software packages that can be useful when managing OpenStack
components. Some examples include:</para>
<itemizedlist>
<listitem>
<para>
Software to provide load balancing
</para>
</listitem>
<listitem>
<para>
Network redundancy protocols
</para>
</listitem>
<listitem>
<para>
Routing daemons
</para>
</listitem>
</itemizedlist>
<para>Some of these software packages are described
in more detail in the <citetitle>OpenStack High Availability
Guide</citetitle> (refer to the <link
xlink:href="http://docs.openstack.org/ha-guide/networking-ha.html">Network
controller cluster stack chapter</link> of the OpenStack High
Availability Guide).</para>
<para>For a general purpose OpenStack cloud, the OpenStack
infrastructure components need to be highly available. If
the design does not include hardware load balancing,
networking software packages like HAProxy will need to be
included.</para>
</section>
<section xml:id="management-software">
<title>Management software</title>
<para>Selected supplemental software solution impacts and
affects the overall OpenStack cloud design. This includes
software for providing clustering, logging, monitoring and
alerting.</para>
<para>Inclusion of clustering software, such as Corosync or
Pacemaker, is determined primarily by the availability
requirements. The impact of including (or not
including) these software packages is primarily determined by
the availability of the cloud infrastructure and the
complexity of supporting the configuration after it is
deployed. The <link xlink:href="http://docs.openstack.org/ha-guide/"><citetitle>OpenStack High Availability Guide</citetitle></link>
provides more
details on the installation and configuration of Corosync and
Pacemaker, should these packages need to be included in the
design.</para>
<para>Requirements for logging, monitoring, and alerting are
determined by operational considerations. Each of these
sub-categories includes a number of various options.</para>
<para>If these software packages are required, the
design must account for the additional resource consumption
(CPU, RAM, storage, and network bandwidth). Some other potential
design impacts include:</para>
<itemizedlist>
<listitem>
<para>OS-hypervisor combination: Ensure that the
selected logging, monitoring, or alerting tools
support the proposed OS-hypervisor combination.</para>
</listitem>
<listitem>
<para>Network hardware: The network hardware selection
needs to be supported by the logging, monitoring, and
alerting software.</para>
</listitem>
</itemizedlist>
</section>
<section xml:id="database-software">
<title>Database software</title>
<para>OpenStack components often require access
to back-end database services to store state and configuration
information. Selecting an appropriate back-end database
that satisfies the availability and fault tolerance
requirements of the OpenStack services is required. OpenStack
services supports connecting to a database that is supported
by the SQLAlchemy python drivers, however, most common
database deployments make use of MySQL or variations of it. We
recommend that the database, which provides back-end
service within a general purpose cloud, be made highly
available when using an available technology which can
accomplish that goal.</para>
</section>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="operational-considerations-general-purpose">
<?dbhtml stop-chunking?>
<title>Operational considerations</title>
<para>In the planning and design phases of the build out, it is
important to include the operation's function. Operational
factors affect the design choices for a general purpose cloud,
and operations staff are often tasked with the maintenance of
cloud environments for larger installations.</para>
<para>Expectations set by the Service Level Agreements (SLAs) directly
affect knowing when and where you should implement redundancy and
high availability. SLAs are contractual
obligations that provide assurances for service availability.
They define the levels of availability that drive the technical
design, often with penalties for not meeting contractual obligations.</para>
<para>SLA terms that affect design include:</para>
<itemizedlist>
<listitem>
<para>API availability guarantees implying multiple
infrastructure services and highly available
load balancers.</para>
</listitem>
<listitem>
<para>Network uptime guarantees affecting switch
design, which might require redundant switching and
power.</para>
</listitem>
<listitem>
<para>Factor in networking security policy requirements
in to your deployments.</para>
</listitem>
</itemizedlist>
<section xml:id="support-and-maintainability-general-purpose">
<title>Support and maintainability</title>
<para>To be able to support and maintain an installation, OpenStack
cloud management requires operations staff to understand and
comprehend design architecture content. The operations and engineering
staff skill level, and level of separation, are dependent on size and
purpose of the installation. Large cloud service providers, or telecom
providers, are more likely to be managed by specially trained, dedicated
operations organizations. Smaller implementations are more likely to rely
on support staff that need to take on combined engineering, design and
operations functions.</para>
<para>Maintaining OpenStack installations requires a
variety of technical skills. You may want to consider using a third-party
management company with special expertise in managing
OpenStack deployment.</para>
</section>
<section xml:id="monitoring-general-purpose">
<title>Monitoring</title>
<para>OpenStack clouds require appropriate monitoring platforms to
ensure errors are caught and managed appropriately. Specific
meters that are critically important to monitor include:</para>
<itemizedlist>
<listitem>
<para>
Image disk utilization
</para>
</listitem>
<listitem>
<para>
Response time to the Compute API
</para>
</listitem>
</itemizedlist>
<para>Leveraging existing monitoring systems is an effective check to
ensure OpenStack environments can be monitored.</para>
</section>
<section xml:id="downtime-general-purpose">
<title>Downtime</title>
<para>To effectively run cloud installations, initial downtime planning
includes creating processes and architectures that support
the following:</para>
<itemizedlist>
<listitem>
<para>
Planned (maintenance)
</para>
</listitem>
<listitem>
<para>
Unplanned (system faults)
</para>
</listitem>
</itemizedlist>
<para>Resiliency of overall system and individual components are going
to be dictated by the requirements of the SLA, meaning designing
for high availability (HA) can have cost ramifications.</para>
</section>
<section xml:id="capacity-planning">
<title>Capacity planning</title>
<para>Capacity constraints for a general purpose cloud environment
include:</para>
<itemizedlist>
<listitem>
<para>
Compute limits
</para>
</listitem>
<listitem>
<para>
Storage limits
</para>
</listitem>
</itemizedlist>
<para>A relationship exists between the size of the compute environment
and the supporting OpenStack infrastructure controller nodes requiring
support.</para>
<para>Increasing the size of the supporting compute environment increases
the network traffic and messages, adding load to the controller or
networking nodes. Effective monitoring of the environment will help
with capacity decisions on scaling.</para>
<para>Compute nodes automatically attach to OpenStack clouds, resulting in
a horizontally scaling process when adding extra compute capacity to an
OpenStack cloud. Additional processes are required to place nodes into
appropriate availability zones and host aggregates. When adding additional
compute nodes to environments, ensure identical or functional compatible
CPUs are used, otherwise live migration features will break. It is necessary
to add rack capacity or network switches as scaling out compute hosts directly
affects network and datacenter resources.</para>
<para>Assessing the average workloads and increasing the number of instances
that can run within the compute environment by adjusting the overcommit
ratio is another option. It is important to remember that changing the CPU overcommit
ratio can have a detrimental effect and cause a potential increase in a
noisy neighbor. The additional risk of increasing the overcommit ratio is
more instances failing when a compute host fails.</para>
<para>Compute host components can also be upgraded to account for
increases in demand; this is known as vertical scaling.
Upgrading CPUs with more cores, or increasing the overall
server memory, can add extra needed capacity depending on
whether the running applications are more CPU intensive or
memory intensive.</para>
<para>Insufficient disk capacity could also have a negative effect
on overall performance including CPU and memory usage.
Depending on the back-end architecture of the OpenStack Block
Storage layer, capacity includes adding disk shelves to
enterprise storage systems or installing additional block
storage nodes. Upgrading directly attached storage installed in
compute hosts, and adding capacity to the shared storage for
additional ephemeral storage to instances, may be necessary.</para>
<para>
For a deeper discussion on many of these topics, refer to the
<link
xlink:href="http://docs.openstack.org/ops"><citetitle>OpenStack
Operations Guide</citetitle></link>.
</para>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="prescriptive-example-online-classifieds">
<?dbhtml stop-chunking?>
<title>Prescriptive example</title>
<para>An online classified advertising company wants to run web applications
consisting of Tomcat, Nginx and MariaDB in a private cloud. To be able
to meet policy requirements, the cloud infrastructure will run in their
own data center. The company has predictable load requirements, but requires
scaling to cope with nightly increases in demand. Their current environment
does not have the flexibility to align with their goal of running an open
source API environment. The current environment consists of the following:</para>
<itemizedlist>
<listitem>
<para>Between 120 and 140 installations of Nginx and
Tomcat, each with 2 vCPUs and 4 GB of RAM</para>
</listitem>
<listitem>
<para>A three-node MariaDB and Galera cluster, each with 4
vCPUs and 8 GB RAM</para>
</listitem>
</itemizedlist>
<para>The company runs hardware load balancers and multiple web
applications serving their websites, and orchestrates environments
using combinations of scripts and Puppet. The website generates large amounts of
log data daily that requires archiving.</para>
<para>The solution would consist of the following OpenStack
components:</para>
<itemizedlist>
<listitem>
<para>A firewall, switches and load balancers on the
public facing network connections.</para>
</listitem>
<listitem>
<para>OpenStack Controller service running Image,
Identity, Networking, combined with support services such as
MariaDB and RabbitMQ, configured for high availability on at
least three controller nodes.</para>
</listitem>
<listitem>
<para>OpenStack Compute nodes running the KVM
hypervisor.</para>
</listitem>
<listitem>
<para>OpenStack Block Storage for use by compute instances,
requiring persistent storage (such as databases for
dynamic sites).</para>
</listitem>
<listitem>
<para>OpenStack Object Storage for serving static objects
(such as images).</para>
</listitem>
</itemizedlist>
<mediaobject><imageobject><imagedata contentwidth="4in"
fileref="../figures/General_Architecture3.png"
/></imageobject></mediaobject>
<para>Running up to 140
web instances and the small number of MariaDB instances
requires 292 vCPUs available, as well as 584 GB RAM. On a
typical 1U server using dual-socket hex-core Intel CPUs with
Hyperthreading, and assuming 2:1 CPU overcommit ratio, this
would require 8 OpenStack Compute nodes.</para>
<para>The web application instances run from local storage on each
of the OpenStack Compute nodes. The web application instances
are stateless, meaning that any of the instances can fail and
the application will continue to function.</para>
<para>MariaDB server instances store their data on shared
enterprise storage, such as NetApp or Solidfire devices. If a
MariaDB instance fails, storage would be expected to be
re-attached to another instance and rejoined to the Galera
cluster.</para>
<para>Logs from the web application servers are shipped to
OpenStack Object Storage for processing and
archiving.</para>
<para>Additional capabilities can be realized by
moving static web content to be served from OpenStack Object
Storage containers, and backing the OpenStack Image service
with OpenStack Object Storage.</para>
<note>
<para>
Increasing OpenStack Object Storage means network bandwidth
needs to be taken into consideration. Running OpenStack Object
Storage with network connections offering 10 GbE or better connectivity
is advised.
</para>
</note>
<para>Leveraging Orchestration and Telemetry services is also a potential issue when
providing auto-scaling, orchestrated web application environments.
Defining the web applications in <glossterm
baseform="Heat Orchestration Template (HOT)">Heat Orchestration Templates (HOT)</glossterm>
negates the reliance on the current scripted Puppet solution.</para>
<para>OpenStack Networking can be used to control hardware load
balancers through the use of plug-ins and the Networking API.
This allows users to control hardware load balance pools
and instances as members in these pools, but their use in
production environments must be carefully weighed against
current stability.</para>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE section [
<!ENTITY % openstack SYSTEM "../../common/entities/openstack.ent">
%openstack;
]>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="technical-considerations-general-purpose">
<?dbhtml stop-chunking?>
<title>Technical considerations</title>
<para>General purpose clouds are expected to
include these base services:</para>
<itemizedlist>
<listitem>
<para>
Compute
</para>
</listitem>
<listitem>
<para>
Network
</para>
</listitem>
<listitem>
<para>
Storage
</para>
</listitem>
</itemizedlist>
<para>Each of these services have different resource requirements.
As a result, you must make design decisions relating directly
to the service, as well as provide a balanced infrastructure for
all services.</para>
<para>Take into consideration the unique aspects of each service, as
individual characteristics and service mass can impact the hardware
selection process. Hardware designs should be generated for each of the
services.</para>
<para>Hardware decisions are also made in relation to network architecture
and facilities planning. These factors play heavily into
the overall architecture of an OpenStack cloud.</para>
<section xml:id="designing-compute-resources-tech-considerations">
<title>Compute resource design</title>
<para>When designing compute resource pools, a number of factors
can impact your design decisions. Factors such as number of processors,
amount of memory, and the quantity of storage required for each hypervisor
must be taken into account.</para>
<para>You will also need to decide whether to provide compute resources
in a single pool or in multiple pools. In most cases, multiple pools
of resources can be allocated and addressed on demand. A compute design
that allocates multiple pools of resources makes best use of application
resources, and is commonly referred to as
<firstterm>bin packing</firstterm>.</para>
<para>In a bin packing design, each independent resource pool provides service
for specific flavors. This helps to ensure that, as instances are scheduled
onto compute hypervisors, each independent node's resources will be allocated
in a way that makes the most efficient use of the available hardware. Bin
packing also requires a common hardware design, with all hardware nodes within
a compute resource pool sharing a common processor, memory, and storage layout.
This makes it easier to deploy, support, and maintain nodes throughout their
life cycle.</para>
<para>An <firstterm>overcommit ratio</firstterm> is the ratio of available
virtual resources to available physical resources. This ratio is
configurable for CPU and memory. The default CPU overcommit ratio is 16:1, and
the default memory overcommit ratio is 1.5:1. Determining the tuning of the
overcommit ratios during the design phase is important as it has a direct
impact on the hardware layout of your compute nodes.</para>
<para>When selecting a processor, compare features and performance
characteristics. Some processors include features specific to virtualized
compute hosts, such as hardware-assisted virtualization, and technology
related to memory paging (also known as EPT shadowing). These types of features
can have a significant impact on the performance of your virtual machine.</para>
<para>You will also need to consider the compute requirements of non-hypervisor
nodes (sometimes referred to as resource nodes). This includes controller, object
storage, and block storage nodes, and networking services.</para>
<para>The number of processor cores and threads impacts the number of worker
threads which can be run on a resource node. Design decisions must relate
directly to the service being run on it, as well as provide a balanced
infrastructure for all services.</para>
<para>Workload can be unpredictable in a general purpose cloud, so consider
including the ability to add additional compute resource pools on demand.
In some cases, however, the demand for certain instance types or flavors may not
justify individual hardware design. In either case, start by allocating
hardware designs that are capable of servicing the most common instance
requests. If you want to add additional hardware to the overall architecture,
this can be done later.</para>
</section>
<section xml:id="designing-network-resources-tech-considerations">
<title>Designing network resources</title>
<para>OpenStack clouds generally have multiple network segments, with
each segment providing access to particular resources. The network services
themselves also require network communication paths which should
be separated from the other networks. When designing network services
for a general purpose cloud, plan for either a physical or logical
separation of network segments used by operators and tenants. You can also
create an additional network segment for access to internal services such as
the message bus and database used by various services. Segregating these
services onto separate networks helps to protect sensitive data and protects
against unauthorized access to services.</para>
<para>Choose a networking service based on the requirements of your instances.
The architecture and design of your cloud will impact whether you choose
OpenStack Networking(neutron), or legacy networking (nova-network).</para>
<variablelist>
<varlistentry>
<term>Legacy networking (nova-network)</term>
<listitem>
<para>The legacy networking (nova-network) service is primarily a
layer-2 networking service that functions in two modes, which
use VLANs in different ways. In a flat network mode, all
network hardware nodes and devices throughout the cloud are connected
to a single layer-2 network segment that provides access to
application data.</para>
<para>When the network devices in the cloud support segmentation
using VLANs, legacy networking can operate in the second mode. In
this design model, each tenant within the cloud is assigned a
network subnet which is mapped to a VLAN on the physical
network. It is especially important to remember the maximum
number of 4096 VLANs which can be used within a spanning tree
domain. This places a hard limit on the amount of
growth possible within the data center. When designing a
general purpose cloud intended to support multiple tenants, we
recommend the use of legacy networking with VLANs, and
not in flat network mode.</para>
</listitem>
</varlistentry>
</variablelist>
<para>Another consideration regarding network is the fact that
legacy networking is entirely managed by the cloud operator;
tenants do not have control over network resources. If tenants
require the ability to manage and create network resources
such as network segments and subnets, it will be necessary to
install the OpenStack Networking service to provide network
access to instances.</para>
<variablelist>
<varlistentry>
<term>OpenStack Networking (neutron)</term>
<listitem>
<para>OpenStack Networking (neutron) is a first class networking
service that gives full control over creation of virtual
network resources to tenants. This is often accomplished in
the form of tunneling protocols which will establish
encapsulated communication paths over existing network
infrastructure in order to segment tenant traffic. These
methods vary depending on the specific implementation, but
some of the more common methods include tunneling over GRE,
encapsulating with VXLAN, and VLAN tags.</para>
</listitem>
</varlistentry>
</variablelist>
<para>We recommend you design at least three network segments:</para>
<itemizedlist>
<listitem>
<para>The first segment is a public network, used for access to REST APIs
by tenants and operators. The controller nodes and swift
proxies are the only devices connecting to this network segment. In some
cases, this network might also be serviced by hardware load balancers
and other network devices.</para>
</listitem>
<listitem>
<para>The second segment is used by administrators to manage hardware resources.
Configuration management tools also use this for deploying software and
services onto new hardware. In some cases, this network segment might also be
used for internal services, including the message bus and database services.
This network needs to communicate with every hardware node.
Due to the highly sensitive nature of this network segment, you also need to
secure this network from unauthorized access.</para>
</listitem>
<listitem>
<para>The third network segment is used by applications and consumers to access
the physical network, and for users to access applications. This network is
segregated from the one used to access the cloud APIs and is not
capable of communicating directly with the hardware resources in the cloud.
Compute resource nodes and network gateway services which allow application
data to access the physical network from outside of the cloud need to
communicate on this network segment.</para>
</listitem>
</itemizedlist>
</section>
<section xml:id="designing-openstack-object-storage-tech-considerations">
<title>Designing OpenStack Object Storage</title>
<para>When designing hardware resources for OpenStack Object
Storage, the primary goal is to maximize the amount of storage
in each resource node while also ensuring that the cost per
terabyte is kept to a minimum. This often involves utilizing
servers which can hold a large number of spinning disks.
Whether choosing to use 2U server form factors with directly
attached storage or an external chassis that holds a larger
number of drives, the main goal is to maximize the storage
available in each node.</para>
<note>
<para>We do not recommended investing in enterprise class drives
for an OpenStack Object Storage cluster. The consistency and
partition tolerance characteristics of OpenStack Object
Storage ensures that data stays up to date and survives
hardware faults without the use of any specialized data
replication devices.</para>
</note>
<para>One of the benefits of OpenStack Object Storage is the ability
to mix and match drives by making use of weighting within the
swift ring. When designing your swift storage cluster, we
recommend making use of the most cost effective storage
solution available at the time.</para>
<para>To achieve durability and availability of data stored as objects
it is important to design object storage resource pools to ensure they can
provide the suggested availability. Considering rack-level and zone-level
designs to accommodate the number of replicas configured to be stored in the
Object Storage service (the default number of replicas is three) is important
when designing beyond the hardware node level. Each replica of
data should exist in its own availability zone with its own
power, cooling, and network resources available to service
that specific zone.</para>
<para>Object storage nodes should be designed so that the number
of requests does not hinder the performance of the cluster.
The object storage service is a chatty protocol, therefore
making use of multiple processors that have higher core counts
will ensure the IO requests do not inundate the server.</para>
</section>
<section xml:id="designing-openstack-block-storage">
<title>Designing OpenStack Block Storage</title>
<para>When designing OpenStack Block Storage resource nodes, it is
helpful to understand the workloads and requirements that will
drive the use of block storage in the cloud. We recommend designing
block storage pools so that tenants can choose appropriate storage
solutions for their applications. By creating multiple storage pools of different
types, in conjunction with configuring an advanced storage
scheduler for the block storage service, it is possible to
provide tenants with a large catalog of storage services with
a variety of performance levels and redundancy options.</para>
<para>Block storage also takes advantage of a number of enterprise storage
solutions. These are addressed via a plug-in driver developed by the
hardware vendor. A large number of
enterprise storage plug-in drivers ship out-of-the-box with
OpenStack Block Storage (and many more available via third
party channels). General purpose clouds are more likely to use
directly attached storage in the majority of block storage nodes,
deeming it necessary to provide additional levels of service to tenants
which can only be provided by enterprise class storage solutions.</para>
<para>Redundancy and availability requirements impact the decision to use
a RAID controller card in block storage nodes. The input-output per second (IOPS)
demand of your application will influence whether or not you should use a RAID
controller, and which level of RAID is required.
Making use of higher performing RAID volumes is suggested when
considering performance. However, where redundancy of
block storage volumes is more important we recommend
making use of a redundant RAID configuration such as RAID 5 or
RAID 6. Some specialized features, such as automated
replication of block storage volumes, may require the use of
third-party plug-ins and enterprise block storage solutions in
order to provide the high demand on storage. Furthermore,
where extreme performance is a requirement it may also be
necessary to make use of high speed SSD disk drives' high
performing flash storage solutions.</para>
</section>
<section xml:id="software-selection-tech-considerations">
<title>Software selection</title>
<para>The software selection process plays a large role in the
architecture of a general purpose cloud. The following have
a large impact on the design of the cloud:</para>
<itemizedlist>
<listitem>
<para>
Choice of operating system
</para>
</listitem>
<listitem>
<para>
Selection of OpenStack software components
</para>
</listitem>
<listitem>
<para>
Choice of hypervisor
</para>
</listitem>
<listitem>
<para>
Selection of supplemental software
</para>
</listitem>
</itemizedlist>
<para>Operating system (OS) selection plays a large role in the
design and architecture of a cloud. There are a number of OSes
which have native support for OpenStack including:</para>
<itemizedlist>
<listitem>
<para>
Ubuntu
</para>
</listitem>
<listitem>
<para>
Red Hat Enterprise Linux (RHEL)
</para>
</listitem>
<listitem>
<para>
CentOS
</para>
</listitem>
<listitem>
<para>
SUSE Linux Enterprise Server (SLES)
</para>
</listitem>
</itemizedlist>
<note>
<para>Native support is not a constraint on the choice of OS; users are
free to choose just about any Linux distribution (or even
Microsoft Windows) and install OpenStack directly from source
(or compile their own packages). However, many organizations will
prefer to install OpenStack from distribution-supplied packages or
repositories (although using the distribution vendor's OpenStack
packages might be a requirement for support).
</para>
</note>
<para>OS selection also directly influences hypervisor selection.
A cloud architect who selects Ubuntu, RHEL, or SLES has some
flexibility in hypervisor; KVM, Xen, and LXC are supported
virtualization methods available under OpenStack Compute
(nova) on these Linux distributions. However, a cloud architect
who selects Hyper-V is limited to Windows Servers. Similarly, a
cloud architect who selects XenServer is limited to the CentOS-based
dom0 operating system provided with XenServer.</para>
<para>The primary factors that play into OS-hypervisor selection
include:</para>
<variablelist>
<varlistentry>
<term>User requirements</term>
<listitem>
<para>The selection of OS-hypervisor
combination first and foremost needs to support the
user requirements.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Support</term>
<listitem>
<para>The selected OS-hypervisor combination
needs to be supported by OpenStack.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Interoperability</term>
<listitem>
<para>The OS-hypervisor needs to be
interoperable with other features and services in the
OpenStack design in order to meet the user
requirements.</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="hypervisor-tech-considerations">
<title>Hypervisor</title>
<para>OpenStack supports a wide variety of hypervisors, one or
more of which can be used in a single cloud. These hypervisors
include:</para>
<itemizedlist>
<listitem>
<para>KVM (and QEMU)</para>
</listitem>
<listitem>
<para>XCP/XenServer</para>
</listitem>
<listitem>
<para>vSphere (vCenter and ESXi)</para>
</listitem>
<listitem>
<para>Hyper-V</para>
</listitem>
<listitem>
<para>LXC</para>
</listitem>
<listitem>
<para>Docker</para>
</listitem>
<listitem>
<para>Bare-metal</para>
</listitem>
</itemizedlist>
<para>A complete list of supported hypervisors and their
capabilities can be found at
<link xlink:href="https://wiki.openstack.org/wiki/HypervisorSupportMatrix">OpenStack Hypervisor Support Matrix</link>.
</para>
<para>We recommend general purpose clouds use hypervisors that
support the most general purpose use cases, such as KVM and
Xen. More specific hypervisors should be chosen to account
for specific functionality or a supported feature requirement.
In some cases, there may also be a mandated
requirement to run software on a certified hypervisor
including solutions from VMware, Microsoft, and Citrix.</para>
<para>The features offered through the OpenStack cloud platform
determine the best choice of a hypervisor. Each hypervisor
has their own hardware requirements which may affect the decisions
around designing a general purpose cloud.</para>
<para>In a mixed hypervisor environment, specific aggregates of
compute resources, each with defined capabilities, enable
workloads to utilize software and hardware specific to their
particular requirements. This functionality can be exposed
explicitly to the end user, or accessed through defined
metadata within a particular flavor of an instance.</para>
</section>
<section xml:id="openstack-components-tech-considerations">
<title>OpenStack components</title>
<para>A general purpose OpenStack cloud design should incorporate
the core OpenStack services to provide a wide range of
services to end-users. The OpenStack core services recommended
in a general purpose cloud are:</para>
<itemizedlist>
<listitem>
<para>OpenStack <glossterm>Compute</glossterm>
(<glossterm>nova</glossterm>)</para>
</listitem>
<listitem>
<para>OpenStack <glossterm>Networking</glossterm>
(<glossterm>neutron</glossterm>)</para>
</listitem>
<listitem>
<para>OpenStack <glossterm>Image service</glossterm>
(<glossterm>glance</glossterm>)</para>
</listitem>
<listitem>
<para>OpenStack <glossterm>Identity</glossterm>
(<glossterm>keystone</glossterm>)</para>
</listitem>
<listitem>
<para>OpenStack <glossterm>dashboard</glossterm>
(<glossterm>horizon</glossterm>)</para>
</listitem>
<listitem>
<para><glossterm>Telemetry</glossterm>
(<glossterm>ceilometer</glossterm>)</para>
</listitem>
</itemizedlist>
<para>A general purpose cloud may also include OpenStack
<glossterm>Object Storage</glossterm> (<glossterm>swift</glossterm>).
OpenStack <glossterm>Block Storage</glossterm>
(<glossterm>cinder</glossterm>). These may be
selected to provide storage to applications and
instances.</para>
</section>
<section xml:id="supplemental-software-tech-considerations">
<title>Supplemental software</title>
<para>A general purpose OpenStack deployment consists of more than
just OpenStack-specific components. A typical deployment
involves services that provide supporting functionality,
including databases and message queues, and may also involve
software to provide high availability of the OpenStack
environment. Design decisions around the underlying message
queue might affect the required number of controller services,
as well as the technology to provide highly resilient database
functionality, such as MariaDB with Galera. In such a
scenario, replication of services relies on quorum.</para>
<para>Where many general purpose deployments use hardware load
balancers to provide highly available API access and SSL
termination, software solutions, for example HAProxy, can also
be considered. It is vital to ensure that such software
implementations are also made highly available. High
availability can be achieved by using software such as
Keepalived or Pacemaker with Corosync. Pacemaker and Corosync
can provide active-active or active-passive highly available
configuration depending on the specific service in the
OpenStack environment. Using this software can affect the
design as it assumes at least a 2-node controller
infrastructure where one of those nodes may be running certain
services in standby mode.</para>
<para>Memcached is a distributed memory object caching system, and
Redis is a key-value store. Both are deployed on
general purpose clouds to assist in alleviating load to the
Identity service. The memcached service caches tokens, and due
to its distributed nature it can help alleviate some
bottlenecks to the underlying authentication system. Using
memcached or Redis does not affect the overall design of your
architecture as they tend to be deployed onto the
infrastructure nodes providing the OpenStack services.</para>
</section>
<section xml:id="controller-infrastructure-tech-considerations">
<title>Controller infrastructure</title>
<para>The Controller infrastructure nodes provide management
services to the end-user as well as providing services
internally for the operating of the cloud. The Controllers
run message queuing services that carry system
messages between each service. Performance issues related to
the message bus would lead to delays in sending that message
to where it needs to go. The result of this condition would be
delays in operation functions such as spinning up and deleting
instances, provisioning new storage volumes and managing
network resources. Such delays could adversely affect an
application’s ability to react to certain conditions,
especially when using auto-scaling features. It is important
to properly design the hardware used to run the controller
infrastructure as outlined above in the Hardware Selection
section.</para>
<para>Performance of the controller services is not limited
to processing power, but restrictions may emerge in serving
concurrent users. Ensure that the APIs and Horizon services
are load tested to ensure that you are able to serve your
customers. Particular attention should be made to the
OpenStack Identity Service (Keystone), which provides the
authentication and authorization for all services, both
internally to OpenStack itself and to end-users. This service
can lead to a degradation of overall performance if this is
not sized appropriately.</para>
</section>
<section xml:id="network-performance-tech-considerations">
<title>Network performance</title>
<para>In a general purpose OpenStack cloud, the requirements of
the network help determine performance capabilities.
It is possible to design OpenStack
environments that run a mix of networking capabilities. By
utilizing the different interface speeds, the users of the
OpenStack environment can choose networks that are fit for
their purpose.</para>
<para>Network performance can be boosted considerably by
implementing hardware load balancers to provide front-end
service to the cloud APIs. The hardware load balancers also
perform SSL termination if that is a requirement of your
environment. When implementing SSL offloading, it is important
to understand the SSL offloading capabilities of the devices
selected.</para>
</section>
<section xml:id="compute-host-tech-considerations">
<title>Compute host</title>
<para>The choice of hardware specifications used in compute nodes
including CPU, memory and disk type directly affects the
performance of the instances. Other factors which can directly
affect performance include tunable parameters within the
OpenStack services, for example the overcommit ratio applied
to resources. The defaults in OpenStack Compute set a 16:1
over-commit of the CPU and 1.5 over-commit of the memory.
Running at such high ratios leads to an increase in
"noisy-neighbor" activity. Care must be taken when sizing your
Compute environment to avoid this scenario. For running
general purpose OpenStack environments it is possible to keep
to the defaults, but make sure to monitor your environment as
usage increases.</para>
</section>
<section xml:id="storage-performance-tech-considerations">
<title>Storage performance</title>
<para>When considering performance of OpenStack Block Storage,
hardware and architecture choice is important. Block Storage
can use enterprise back-end systems such as NetApp or EMC,
scale out storage such as GlusterFS and Ceph, or simply use
the capabilities of directly attached storage in the nodes
themselves. Block Storage may be deployed so that traffic
traverses the host network, which could affect, and be
adversely affected by, the front-side API traffic performance.
As such, consider using a dedicated data storage network with
dedicated interfaces on the Controller and Compute
hosts.</para>
<para>When considering performance of OpenStack Object Storage, a
number of design choices will affect performance. A user’s
access to the Object Storage is through the proxy services,
which sit behind hardware load balancers. By the
very nature of a highly resilient storage system, replication
of the data would affect performance of the overall system. In
this case, 10 GbE (or better) networking is recommended
throughout the storage network architecture.</para>
</section>
<section xml:id="availability-tech-considerations">
<title>Availability</title>
<para>In OpenStack, the infrastructure is integral to providing
services and should always be available, especially when
operating with SLAs. Ensuring network availability is
accomplished by designing the network architecture so that no
single point of failure exists. A consideration of the number
of switches, routes and redundancies of power should be
factored into core infrastructure, as well as the associated
bonding of networks to provide diverse routes to your highly
available switch infrastructure.</para>
<para>The OpenStack services themselves should be deployed across
multiple servers that do not represent a single point of
failure. Ensuring API availability can be achieved by placing
these services behind highly available load balancers that
have multiple OpenStack servers as members.</para>
<para>OpenStack lends itself to deployment in a highly available
manner where it is expected that at least 2 servers be
utilized. These can run all the services involved from the
message queuing service, for example RabbitMQ or QPID, and an
appropriately deployed database service such as MySQL or
MariaDB. As services in the cloud are scaled out, back-end
services will need to scale too. Monitoring and reporting on
server utilization and response times, as well as load testing
your systems, will help determine scale out decisions.</para>
<para>Care must be taken when deciding network functionality.
Currently, OpenStack supports both the legacy networking (nova-network)
system and the newer, extensible OpenStack Networking (neutron). Both
have their pros and cons when it comes to providing highly
available access. Legacy networking, which provides networking
access maintained in the OpenStack Compute code, provides a
feature that removes a single point of failure when it comes
to routing, and this feature is currently missing in OpenStack
Networking. The effect of legacy networking’s multi-host
functionality restricts failure domains to the host running
that instance.</para>
<para>When using OpenStack Networking, the
OpenStack controller servers or separate Networking
hosts handle routing. For a deployment that requires features
available in only Networking, it is possible to
remove this restriction by using third party software that
helps maintain highly available L3 routes. Doing so allows for
common APIs to control network hardware, or to provide complex
multi-tier web applications in a secure manner. It is also
possible to completely remove routing from
Networking, and instead rely on hardware routing capabilities.
In this case, the switching infrastructure must support L3
routing.</para>
<para>OpenStack Networking and legacy networking
both have their advantages and
disadvantages. They are both valid and supported options that
fit different network deployment models described in the
<citetitle><link
xlink:href="http://docs.openstack.org/openstack-ops/content/network_design.html#network_deployment_options"
>OpenStack Operations Guide</link></citetitle>.</para>
<para>Ensure your deployment has adequate back-up capabilities.</para>
<para>Application design must also be factored into the
capabilities of the underlying cloud infrastructure. If the
compute hosts do not provide a seamless live migration
capability, then it must be expected that when a compute host
fails, that instance and any data local to that instance will
be deleted. However, when providing an expectation to users
that instances have a high-level of uptime guarantees, the
infrastructure must be deployed in a way that eliminates any
single point of failure when a compute host disappears. This
may include utilizing shared file systems on enterprise
storage or OpenStack Block storage to provide a level of
guarantee to match service features.</para>
<para>For more information on high availability in OpenStack, see the <link
xlink:href="http://docs.openstack.org/ha-guide/"><citetitle>OpenStack
High Availability Guide</citetitle></link>.
</para>
</section>
<section xml:id="security-tech-considerations">
<title>Security</title>
<para>A security domain comprises users, applications, servers or
networks that share common trust requirements and expectations
within a system. Typically they have the same authentication
and authorization requirements and users.</para>
<para>These security domains are:</para>
<itemizedlist>
<listitem>
<para>Public</para>
</listitem>
<listitem>
<para>Guest</para>
</listitem>
<listitem>
<para>Management</para>
</listitem>
<listitem>
<para>Data</para>
</listitem>
</itemizedlist>
<para>These security domains can be mapped to an OpenStack
deployment individually, or combined. In each case, the cloud operator
should be aware of the appropriate security concerns. Security
domains should be mapped out against your specific OpenStack
deployment topology. The domains and their trust requirements
depend upon whether the cloud instance is public, private, or
hybrid.</para>
<itemizedlist>
<listitem>
<para>The public security domain is an entirely untrusted area of
the cloud infrastructure. It can refer to the internet as a
whole or simply to networks over which you have no authority.
This domain should always be considered untrusted.</para>
</listitem>
<listitem>
<para>The guest security domain handles compute data generated by
instances on the cloud but not services that support the
operation of the cloud, such as API calls. Public cloud
providers and private cloud providers who do not have
stringent controls on instance use or who allow unrestricted
internet access to instances should consider this domain to be
untrusted. Private cloud providers may want to consider this
network as internal and therefore trusted only if they have
controls in place to assert that they trust instances and all
their tenants.</para>
</listitem>
<listitem>
<para>The management security domain is where services interact.
Sometimes referred to as the <emphasis>control plane</emphasis>, the networks
in this domain transport confidential data such as configuration
parameters, user names, and passwords. In most deployments this
domain is considered trusted.</para>
</listitem>
<listitem>
<para>The data security domain is concerned primarily with
information pertaining to the storage services within
OpenStack. Much of the data that crosses this network has high
integrity and confidentiality requirements and, depending on
the type of deployment, may also have strong availability
requirements. The trust level of this network is heavily
dependent on other deployment decisions.</para>
</listitem>
</itemizedlist>
<para>When deploying OpenStack in an enterprise as a private cloud
it is usually behind the firewall and within the trusted
network alongside existing systems. Users of the cloud are
employees that are bound by the security
requirements set forth by the company. This tends to push most
of the security domains towards a more trusted model. However,
when deploying OpenStack in a public facing role, no
assumptions can be made and the attack vectors significantly
increase.</para>
<para>Consideration must be taken when managing the users of the
system for both public and private clouds. The identity
service allows for LDAP to be part of the authentication
process. Including such systems in an OpenStack deployment may
ease user management if integrating into existing
systems.</para>
<para>It is important to understand that user authentication
requests include sensitive information including user names,
passwords, and authentication tokens. For this reason, placing
the API services behind hardware that performs SSL termination
is strongly recommended.</para>
<para>
For more information OpenStack Security, see the <link
xlink:href="http://docs.openstack.org/security-guide/"><citetitle>OpenStack
Security Guide</citetitle></link>
</para>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="user-requirements-general-purpose">
<?dbhtml stop-chunking?>
<title>User requirements</title>
<para>When building a general purpose cloud, you should follow the
<glossterm baseform="IaaS">Infrastructure-as-a-Service (IaaS)</glossterm>
model; a platform best suited for use cases with simple requirements.
General purpose cloud user requirements are not complex.
However, it is important to capture them even
if the project has minimum business and technical requirements, such as a
proof of concept (PoC), or a small lab platform.</para>
<note>
<para>
The following user considerations are written from the perspective of
the cloud builder, not from the perspective of the end user.
</para>
</note>
<variablelist>
<varlistentry>
<term>Cost</term>
<listitem>
<para>Financial factors are a primary concern for
any organization. Cost is an important criterion
as general purpose clouds are considered the baseline
from which all other cloud architecture environments
derive. General purpose clouds do not always provide
the most cost-effective environment for specialized
applications or situations. Unless razor-thin margins and costs have
been mandated as a critical factor, cost should not be
the sole consideration when choosing or designing a
general purpose architecture.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Time to market</term>
<listitem>
<para>The ability to deliver services or products within
a flexible time frame is a common business factor
when building a general purpose cloud.
Delivering a product in six months instead
of two years is a driving force behind the
decision to build general purpose clouds. General
purpose clouds allow users to self-provision and gain
access to compute, network, and storage resources
on-demand thus decreasing time to market.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Revenue opportunity</term>
<listitem>
<para>Revenue opportunities for a
cloud will vary greatly based on the intended
use case of that particular cloud. Some general
purpose clouds are built for commercial customer
facing products, but there are alternatives
that might make the general purpose cloud the right
choice.</para>
</listitem>
</varlistentry>
</variablelist>
<section xml:id="technical-requirements">
<title>Technical requirements</title>
<para>Technical cloud architecture requirements should be weighted
against the business requirements.
</para>
<variablelist>
<varlistentry>
<term>Performance</term>
<listitem>
<para>As a baseline product, general purpose
clouds do not provide optimized performance for any
particular function. While a general purpose cloud
should provide enough performance to satisfy average
user considerations, performance is not a general
purpose cloud customer driver.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>No predefined usage model</term>
<listitem>
<para>The lack of a pre-defined
usage model enables the user to run a wide variety of
applications without having to know the application
requirements in advance. This provides a degree of
independence and flexibility that no other cloud
scenarios are able to provide.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>On-demand and self-service application</term>
<listitem>
<para>By
definition, a cloud provides end users with the
ability to self-provision computing power, storage,
networks, and software in a simple and flexible way.
The user must be able to scale their resources up to a
substantial level without disrupting the underlying
host operations. One of the benefits of using a
general purpose cloud architecture is the ability to
start with limited resources and increase them over
time as the user demand grows.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Public cloud</term>
<listitem>
<para>For a company interested in building a
commercial public cloud offering based on OpenStack,
the general purpose architecture model might be the
best choice. Designers are not always going to
know the purposes or workloads for which the end users
will use the cloud.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Internal consumption (private) cloud</term>
<listitem>
<para>Organizations need to determine if it is logical to
create their own clouds internally. Using a private cloud,
organizations are able to maintain complete control over
architectural and cloud components.</para>
<note>
<para>Users will want to combine
using the internal cloud with access to an external
cloud. If that case is likely, it might be worth
exploring the possibility of taking a multi-cloud
approach with regard to at least some of the
architectural elements.
</para>
</note>
<para>Designs that incorporate the
use of multiple clouds, such as a private cloud and a
public cloud offering, are described in the
"Multi-Cloud" scenario, see <xref linkend="multi_site"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Security</term>
<listitem>
<para>Security should be implemented according
to asset, threat, and vulnerability risk assessment
matrices. For cloud domains that require increased
computer security, network security, or information
security, a general purpose cloud is not considered an
appropriate choice.</para>
</listitem>
</varlistentry>
</variablelist>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="arch-guide-architecture-hybrid">
<?dbhtml stop-chunking?>
<title>Architecture</title>
<para>Map out the dependencies of the expected workloads
and the cloud infrastructures required to support them to architect a
solution for the broadest compatibility between cloud platforms,
minimizing the need to create workarounds and processes to fill
identified gaps.</para>
<para>For your chosen cloud management platform, note the relative
levels of support for both monitoring and orchestration.</para>
<mediaobject>
<imageobject>
<imagedata contentwidth="4in"
fileref="../figures/Multi-Cloud_Priv-AWS4.png"/>
</imageobject>
</mediaobject>
<section xml:id="image-portability">
<title>Image portability</title>
<para>The majority of cloud workloads currently run on instances
using hypervisor technologies. The challenge is that each of these
hypervisors uses an image format that may not be compatible with the
others. When possible, standardize on a single hypervisor and instance
image format. This may not be possible when using externally-managed
public clouds.</para>
<para>Conversion tools exist to address image format compatibility.
Examples include <link
xlink:href="http://libguestfs.org/virt-v2v">virt-p2v/virt-v2v</link>
and <link
xlink:href="http://libguestfs.org/virt-edit.1.html">
virt-edit</link>. These tools cannot serve beyond basic cloud instance
specifications.</para>
<para>Alternatively, build a thin operating system image as
the base for new instances. This facilitates rapid creation of cloud
instances using cloud orchestration or configuration management tools
for more specific templating. Remember if you intend to use portable
images for disaster recovery, application diversity, or high
availability, your users could move the images and instances between
cloud platforms regularly.</para>
</section>
<section xml:id="upper-layer-services">
<title>Upper-layer services</title>
<para>Many clouds offer complementary services beyond the
basic compute, network, and storage components. These
additional services often simplify the deployment
and management of applications on a cloud platform.</para>
<para>When moving workloads from the source to the destination
cloud platforms, consider that the destination cloud platform
may not have comparable services. Implement workloads in a
different way or by using a different technology.</para>
<para>For example, moving an application that uses a NoSQL database
service such as MongoDB could cause difficulties in maintaining
the application between the platforms.</para>
<para>There are a number of options that are appropriate for
the hybrid cloud use case:</para>
<itemizedlist>
<listitem>
<para>Implementing a baseline of upper-layer services
across all of the cloud platforms. For
platforms that do not support a given service, create
a service on top of that platform and apply it to the
workloads as they are launched on that cloud.</para>
<para>For example, through the <glossterm>Database service</glossterm>
for OpenStack (<glossterm>trove</glossterm>),
OpenStack supports MySQL-as-a-Service but not NoSQL
databases in production. To move from or run
alongside AWS, a NoSQL workload must use an automation
tool, such as the Orchestration service (heat), to
recreate the NoSQL database on top of OpenStack.
</para>
</listitem>
<listitem>
<para>Deploying a <glossterm>Platform-as-a-Service (PaaS)</glossterm>
technology that abstracts the
upper-layer services from the underlying cloud
platform. The unit of application deployment and
migration is the PaaS. It leverages the services of
the PaaS and only consumes the base infrastructure
services of the cloud platform.</para>
</listitem>
<listitem>
<para>Using automation tools to create the required upper-layer services
that are portable across all cloud platforms.</para>
<para>For example, instead of using database services that
are inherent in the cloud platforms, launch cloud
instances and deploy the databases on those
instances using scripts or configuration and
application deployment tools.</para>
</listitem>
</itemizedlist>
</section>
<section xml:id="network-services">
<title>Network services</title>
<para>Network services functionality is a critical component of
multiple cloud architectures. It is an important factor
to assess when choosing a CMP and cloud provider.
Considerations include:</para>
<itemizedlist>
<listitem>
<para>
Functionality
</para>
</listitem>
<listitem>
<para>
Security
</para>
</listitem>
<listitem>
<para>
Scalability
</para>
</listitem>
<listitem>
<para>
High availability (HA)
</para>
</listitem>
</itemizedlist>
<para>Verify and test critical cloud endpoint features.</para>
<itemizedlist>
<listitem>
<para>After selecting the network functionality framework,
you must confirm the functionality is compatible. This
ensures testing and functionality persists
during and after upgrades.</para>
<note>
<para>Diverse cloud platforms may de-synchronize
over time if you do not maintain their mutual compatibility.
This is a particular issue with APIs.</para>
</note>
</listitem>
<listitem>
<para>Scalability across multiple cloud providers determines
your choice of underlying network framework. It is important to
have the network API functions presented and to verify
that the desired functionality persists across all
chosen cloud endpoint.</para>
</listitem>
<listitem>
<para>High availability implementations vary in
functionality and design. Examples of some common
methods are active-hot-standby, active-passive, and
active-active. Develop your high availability
implementation and a test framework to understand
the functionality and limitations of the environment.</para>
</listitem>
<listitem>
<para>It is imperative to address security considerations.
For example, addressing how data is secured between client and
endpoint and any traffic that traverses the multiple clouds.
Business and regulatory requirements dictate what security
approach to take. For more information, see the
<link linkend="security-overview">Security
Requirements Chapter</link></para>
</listitem>
</itemizedlist>
</section>
<section xml:id="data">
<title>Data</title>
<para>Traditionally, replication has been the best method of protecting
object store implementations. A variety of replication methods exist
in storage architectures, for example synchronous and asynchronous
mirroring. Most object stores and back-end storage systems implement
methods for replication at the storage subsystem layer.
Object stores also tailor replication techniques
to fit a cloud's requirements.</para>
<para>Organizations must find the right balance between
data integrity and data availability. Replication strategy may
also influence disaster recovery methods.</para>
<para>Replication across different racks, data centers, and
geographical regions increases focus on
determining and ensuring data locality. The ability to
guarantee data is accessed from the nearest or fastest storage
can be necessary for applications to perform well.</para>
<note>
<para>When running embedded object store methods, ensure that you do
not instigate extra data replication as this can cause performance
issues.</para>
</note>
</section>
</section>

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<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="arch-guide-hybrid-operational-considerations">
<?dbhtml stop-chunking?>
<title>Operational considerations</title>
<para>Hybrid cloud deployments present complex operational
challenges. Differences between provider clouds can cause
incompatibilities with workloads or Cloud Management
Platforms (CMP). Cloud providers may also offer different levels of
integration with competing cloud offerings.</para>
<para>Monitoring is critical to maintaining a hybrid cloud, and it is
important to determine if a CMP supports
monitoring of all the clouds involved, or if compatible APIs
are available to be queried for necessary information.</para>
<section xml:id="agility">
<title>Agility</title>
<para>Hybrid clouds provide application
availability across different cloud environments and
technologies. This availability enables the deployment to
survive disaster in any single cloud environment.
Each cloud should provide the means to create instances quickly
in response to capacity issues or failure elsewhere in the hybrid
cloud.</para>
</section>
<section xml:id="application-readiness-hybrid">
<title>Application readiness</title>
<para>Enterprise workloads that depend on the
underlying infrastructure for availability are not designed to
run on OpenStack. If the application cannot
tolerate infrastructure failures, it is likely to require
significant operator intervention to recover. Applications for
hybrid clouds must be fault tolerant, with an SLA that is not tied
to the underlying infrastructure. Ideally, cloud applications should be
able to recover when entire racks and data centers experience an
outage.</para>
</section>
<section xml:id="upgrades">
<title>Upgrades</title>
<para>If a deployment includes a public cloud, predicting
upgrades may not be possible. Carefully examine provider SLAs.</para>
<note>
<para>At massive scale, even when
dealing with a cloud that offers an SLA with a high percentage
of uptime, workloads must be able to recover quickly.</para>
</note>
<para>When upgrading private cloud deployments, minimize disruption by
making incremental changes and providing a facility to either rollback
or continue to roll forward when using a continuous delivery
model.</para>
<para>You may need to coordinate CMP upgrades with hybrid cloud upgrades if
there are API changes.</para>
</section>
<section xml:id="network-operation-center-noc">
<title>Network Operation Center</title>
<para>Consider infrastructure control
when planning the Network Operation Center (NOC)
for a hybrid cloud environment. If a significant
portion of the cloud is on externally managed systems,
prepare for situations where it may not be possible to
make changes.
Additionally, providers may differ on how
infrastructure must be managed and exposed. This can lead to
delays in root cause analysis where each insists the blame
lies with the other provider.</para>
<para>Ensure that the network structure connects all clouds to form
integrated system, keeping in mind the state of handoffs.
These handoffs must both be as reliable as possible and
include as little latency as possible to ensure the best
performance of the overall system.</para>
</section>
<section xml:id="maintainability">
<title>Maintainability</title>
<para>Hybrid clouds rely on third party systems and processes. As a
result, it is not possible to guarantee
proper maintenance of the overall system. Instead, be prepared to
abandon workloads and recreate them in an improved state.</para>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="prescriptive-examples-multi-cloud">
<?dbhtml stop-chunking?>
<title>Prescriptive examples</title>
<para>Hybrid cloud environments are designed for
these use cases:</para>
<itemizedlist>
<listitem>
<para>Bursting workloads from private to public OpenStack
clouds</para>
</listitem>
<listitem>
<para>Bursting workloads from private to public
non-OpenStack clouds</para>
</listitem>
<listitem>
<para>High availability across clouds (for technical
diversity)</para>
</listitem>
</itemizedlist>
<para>This chapter provides examples of environments
that address each of these use cases.</para>
<section xml:id="bursting-to-public-openstack-cloud">
<title>Bursting to a public OpenStack cloud</title>
<para>Company A's data center is running low on
capacity. It is not possible to expand the data center in the
foreseeable future. In order to accommodate
the continuously growing need for development resources in the
organization, Company A decides to use resources in the public
cloud.</para>
<para>Company A has an established data
center with a substantial amount of hardware. Migrating the
workloads to a public cloud is not feasible.</para>
<para>The company has an internal cloud management platform that
directs requests to the appropriate cloud, depending on
the local capacity. This is a custom in-house application written for
this specific purpose.</para>
<para>This solution is depicted in the figure below:</para>
<mediaobject>
<imageobject>
<imagedata contentwidth="4in"
fileref="../figures/Multi-Cloud_Priv-Pub3.png"
/>
</imageobject>
</mediaobject>
<para>This example shows two clouds with a Cloud Management
Platform (CMP) connecting them. This guide does not
discuss a specific CMP, but describes how the Orchestration and
Telemetry services handle, manage, and control workloads.</para>
<para>The private OpenStack cloud has at least one
controller and at least one compute node. It includes
metering using the Telemetry service. The Telemetry service
captures the load increase and the CMP processes the information.
If there is available capacity, the CMP uses the
OpenStack API to call the Orchestration service. This creates
instances on the private cloud in response to user requests.
When capacity is not available on the private cloud,
the CMP issues a request to the Orchestration service API of
the public cloud. This creates the instance on the public
cloud.</para>
<para>In this example, Company A does not direct the deployments to an
external public cloud due to concerns regarding resource control,
security, and increased operational expense</para>
</section>
<section xml:id="bursting-to-public-nonopenstack-cloud">
<title>Bursting to a public non-OpenStack cloud</title>
<para>The second example examines bursting workloads from the
private cloud into a non-OpenStack public cloud using Amazon
Web Services (AWS) to take advantage of additional capacity
and to scale applications.</para>
<para>The following diagram demonstrates an OpenStack-to-AWS hybrid
cloud:</para>
<mediaobject>
<imageobject>
<imagedata contentwidth="4in"
fileref="../figures/Multi-Cloud_Priv-AWS4.png"
/>
</imageobject>
</mediaobject>
<para>Company B states that its developers are already using AWS and
do not want to change to a different provider.</para>
<para>If the CMP is capable of connecting to an external
cloud provider with an appropriate API, the workflow process
remains the same as the previous scenario. The actions the
CMP takes, such as monitoring loads and creating new instances,
stay the same. However, the CMP performs actions in the
public cloud using applicable API calls.</para>
<para>If the public cloud is AWS, the CMP would use the
EC2 API to create a new instance and assign an Elastic IP.
It can then add that IP to HAProxy in the private cloud.
The CMP can also reference AWS-specific
tools such as CloudWatch and CloudFormation.</para>
<para>Several open source tool kits for building CMPs are
available and can handle this kind of translation. Examples include
ManageIQ, jClouds, and JumpGate.</para>
</section>
<section xml:id="high-availability-disaster-recovery">
<title>High availability and disaster recovery</title>
<para>Company C requires their local data center
to be able to recover from failure. Some of the
workloads currently in use are running on their private
OpenStack cloud. Protecting the data involves Block Storage,
Object Storage, and a database. The architecture
supports the failure of large components of the system while
ensuring that the system continues to deliver services.
While the services remain available to users, the failed
components are restored in the background based on standard
best practice data replication policies. To achieve these objectives,
Company C replicates data to a second cloud in a geographically distant
location. The following diagram describes this system:</para>
<mediaobject>
<imageobject>
<imagedata contentwidth="4in"
fileref="../figures/Multi-Cloud_failover2.png"
/>
</imageobject>
</mediaobject>
<para>This example includes two private OpenStack clouds connected
with a CMP. The source cloud,
OpenStack Cloud 1, includes a controller and at least one
instance running MySQL. It also includes at least one Block
Storage volume and one Object Storage volume. This means that data
is available to the users at all times. The details of the
method for protecting each of these sources of data
differs.</para>
<para>Object Storage relies on the replication capabilities of
the Object Storage provider. Company C enables OpenStack Object Storage
so that it creates geographically separated replicas
that take advantage of this feature. The company configures storage
so that at least one replica exists in each cloud. In order to make
this work, the company configures a single array spanning both clouds
with OpenStack Identity. Using Federated Identity, the array talks
to both clouds, communicating with OpenStack Object Storage
through the Swift proxy.</para>
<para>For Block Storage, the replication is a little more
difficult, and involves tools outside of OpenStack itself. The
OpenStack Block Storage volume is not set as the drive itself
but as a logical object that points to a physical back end. Disaster
recovery is configured for Block Storage for
synchronous backup for the highest level of data protection,
but asynchronous backup could have been set as an alternative
that is not as latency sensitive. For asynchronous backup, the
Block Storage API makes it possible to export the data and also the
metadata of a particular volume, so that it can be moved and
replicated elsewhere. More information can be found here:
<link
xlink:href="https://blueprints.launchpad.net/cinder/+spec/cinder-backup-volume-metadata-support">
https://blueprints.launchpad.net/cinder/+spec/cinder-backup-volume-metadata-support</link>.
</para>
<para>The synchronous backups create an identical volume in both
clouds and chooses the appropriate flavor so that each cloud
has an identical back end. This is done by creating volumes
through the CMP. After this is configured, a solution
involving DRDB synchronizes the physical drives.</para>
<para>The database component is backed up using synchronous
backups. MySQL does not support geographically diverse
replication, so disaster recovery is provided by replicating
the file itself. As it is not possible to use Object Storage
as the back end of a database like MySQL, Swift replication
is not an option. Company C decides not to store the data on
another geo-tiered storage system, such as Ceph, as Block
Storage. This would have given another layer of protection.
Another option would have been to store the database on an
OpenStack Block Storage volume and backing it up like any
other Block Storage.</para>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE section [
<!ENTITY % openstack SYSTEM "../../common/entities/openstack.ent">
%openstack;
]>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="technical-considerations-hybrid">
<?dbhtml stop-chunking?>
<title>Technical considerations</title>
<para>A hybrid cloud environment requires inspection and
understanding of technical issues in external data centers that may
not be in your control. Ideally, select an architecture
and CMP that are adaptable to changing environments.</para>
<para>Using diverse cloud platforms increases the risk of compatibility
issues, but clouds using the same version and distribution
of OpenStack are less likely to experience problems.</para>
<para>Clouds that exclusively use the same versions of OpenStack should
have no issues, regardless of distribution. More recent distributions
are less likely to encounter incompatibility between versions. An
OpenStack community initiative defines core functions that need to
remain backward compatible between supported versions. For example, the
DefCore initiative defines basic functions that every distribution must
support in order to use the name <productname>OpenStack</productname>.
</para>
<para>Vendors can add proprietary customization to their distributions. If
an application or architecture makes use of these features, it can be
difficult to migrate to or use other types of environments.</para>
<para>If an environment includes non-OpenStack clouds, it may experience
compatibility problems. CMP tools must account for the differences in
the handling of operations and the implementation of services.</para>
<itemizedlist>
<title>Possible cloud incompatibilities</title>
<listitem>
<para>Instance deployment</para>
</listitem>
<listitem>
<para>Network management</para>
</listitem>
<listitem>
<para>Application management</para>
</listitem>
<listitem>
<para>Services implementation</para>
</listitem>
</itemizedlist>
<section xml:id="capacity-planning-hybrid">
<title>Capacity planning</title>
<para>One of the primary reasons many organizations use a
hybrid cloud is to increase capacity without making large capital
investments.</para>
<para>Capacity and the placement of workloads are key design considerations
for hybrid clouds. The long-term capacity plan for these
designs must incorporate growth over time to prevent permanent
consumption of more expensive external clouds. To avoid this scenario,
account for future applications' capacity requirements and plan growth
appropriately.</para>
<para>It is difficult to predict the amount of load a particular
application might incur if the number of users fluctuates, or the
application experiences an unexpected increase in use. It is
possible to define application requirements in terms of vCPU, RAM,
bandwidth, or other resources and plan appropriately. However, other
clouds might not use the same meter or even the same oversubscription
rates.</para>
<para>Oversubscription is a method to emulate more capacity than
may physically be present. For example, a physical
hypervisor node with 32&nbsp;GB RAM may host 24
instances, each provisioned with 2&nbsp;GB RAM. As long
as all 24 instances do not concurrently use 2 full
gigabytes, this arrangement works well. However, some
hosts take oversubscription to extremes and, as a result,
performance can be inconsistent. If at all
possible, determine what the oversubscription rates of each
host are and plan capacity accordingly.</para>
</section>
<section xml:id="utilization-hybrid">
<title>Utilization</title>
<para>A CMP must be aware of what workloads are running, where they are
running, and their preferred utilizations. For example, in
most cases it is desirable to run as many workloads internally
as possible, utilizing other resources only when necessary. On
the other hand, situations exist in which the opposite is
true, such as when an internal cloud is only for development and
stressing it is undesirable. A cost model of various scenarios and
consideration of internal priorities helps with this decision. To
improve efficiency, automate these decisions when possible.</para>
<para>The Telemetry service (ceilometer) provides information on the usage
of various OpenStack components. Note the following:</para>
<itemizedlist>
<listitem>
<para>
If Telemetry must retain a large amount of data, for
example when monitoring a large or active cloud, we recommend
using a NoSQL back end such as MongoDB.</para>
</listitem>
<listitem>
<para>
You must monitor connections to non-OpenStack clouds
and report this information to the CMP.</para>
</listitem>
</itemizedlist>
</section>
<section xml:id="performance-hybrid">
<title>Performance</title>
<para>Performance is critical to hybrid cloud deployments, and they are
affected by many of the same issues as multi-site deployments,
such as network latency between sites. Also consider the time required
to run a workload in different clouds and methods for reducing this
time. This may require moving data closer to applications
or applications closer to the data they process, and
grouping functionality so that connections that
require low latency take place over a single cloud rather than
spanning clouds. This may also require a CMP that can determine which
cloud can most efficiently run which types of workloads.</para>
<para>As with utilization, native OpenStack tools help improve performance.
For example, you can use Telemetry to measure performance and the
Orchestration service (heat) to react to changes in demand.</para>
<note>
<para>Orchestration requires special client configurations to integrate
with Amazon Web Services. For other types of clouds, use CMP
features.
</para>
</note>
</section>
<section xml:id="components">
<title>Components</title>
<para>Using more than one cloud in any design requires consideration of
four OpenStack tools:</para>
<variablelist>
<varlistentry>
<term>OpenStack Compute (nova)</term>
<listitem>
<para>Regardless of deployment location, hypervisor choice has a
direct effect on how difficult it is to integrate with
additional clouds.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Networking (neutron)</term>
<listitem>
<para>Whether using OpenStack Networking (neutron) or legacy
networking (nova-network), it is necessary to understand
network integration capabilities in order to
connect between clouds.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Telemetry (ceilometer)</term>
<listitem>
<para>Use of Telemetry depends, in large part, on what the other
parts of the cloud you are using.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Orchestration (heat)</term>
<listitem>
<para>Orchestration can be a valuable tool in orchestrating tasks a
CMP decides are necessary in an OpenStack-based cloud.</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="special-considerations-hybrid">
<title>Special considerations</title>
<para>Hybrid cloud deployments require consideration of two issues that
are not common in other situations:</para>
<variablelist>
<varlistentry>
<term>Image portability</term>
<listitem>
<para>As of the Kilo release, there is no common image format that is
usable by all clouds. Conversion or recreation of images is necessary
if migrating between clouds. To simplify deployment, use the smallest
and simplest images feasible, install only what is necessary, and
use a deployment manager such as Chef or Puppet. Do not use golden
images to speed up the process unless you repeatedly deploy the same
images on the same cloud.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>API differences</term>
<listitem>
<para>Avoid using a hybrid cloud deployment with more than just
OpenStack (or with different versions of OpenStack) as API changes
can cause compatibility issues.</para>
</listitem>
</varlistentry>
</variablelist>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="user-requirements-hybrid">
<?dbhtml stop-chunking?>
<title>User requirements</title>
<para>Hybrid cloud architectures are complex, especially those
that use heterogeneous cloud platforms. Ensure that design choices
match requirements so that the benefits outweigh the inherent additional
complexity and risks.</para>
<variablelist>
<title>Business considerations when designing a hybrid
cloud deployment</title>
<varlistentry>
<term>Cost</term>
<listitem>
<para>A hybrid cloud architecture involves multiple
vendors and technical architectures. These
architectures may be more expensive to deploy and
maintain. Operational costs can be higher because of
the need for more sophisticated orchestration and
brokerage tools than in other architectures. In
contrast, overall operational costs might be lower by
virtue of using a cloud brokerage tool to deploy the
workloads to the most cost effective platform.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Revenue opportunity</term>
<listitem>
<para>Revenue opportunities vary based on the intent and use case
of the cloud. As a commercial, customer-facing product, you
must consider whether building over multiple platforms makes
the design more attractive to customers.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Time-to-market</term>
<listitem>
<para>One common reason to use cloud platforms is to improve the
time-to-market of a new product or application. For example,
using multiple cloud platforms is viable because there is an
existing investment in several applications. It is faster to
tie the investments together rather than migrate the
components and refactoring them to a single platform.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Business or technical diversity</term>
<listitem>
<para>Organizations leveraging cloud-based services can
embrace business diversity and utilize a hybrid cloud
design to spread their workloads across multiple cloud
providers. This ensures that no single cloud provider is
the sole host for an application.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Application momentum</term>
<listitem>
<para>Businesses with existing applications may find that it is
more cost effective to integrate applications on multiple
cloud platforms than migrating them to a single platform.</para>
</listitem>
</varlistentry>
</variablelist>
<section xml:id="workload-considerations">
<title>Workload considerations</title>
<para>A workload can be a single application or a suite of applications
that work together. It can also be a duplicate set of applications that
need to run on multiple cloud environments. In a hybrid cloud
deployment, the same workload often needs to function
equally well on radically different public and private cloud
environments. The architecture needs to address these
potential conflicts, complexity, and platform
incompatibilities.</para>
<variablelist>
<title>Use cases for a hybrid cloud architecture</title>
<varlistentry>
<term>Dynamic resource expansion or bursting</term>
<listitem>
<para>An application that requires additional resources may suit
a multiple cloud architecture.
For example, a retailer needs additional resources
during the holiday season, but does not want to add private
cloud resources to meet the peak demand. The user can
accommodate the increased load by bursting to
a public cloud for these peak load
periods. These bursts could be for long or short
cycles ranging from hourly to yearly.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Disaster recovery and business continuity</term>
<listitem>
<para>Cheaper storage makes the public
cloud suitable for maintaining backup applications.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Federated hypervisor and instance management</term>
<listitem>
<para>Adding self-service, charge back, and transparent delivery of
the resources from a federated pool can be cost
effective. In a hybrid cloud environment, this is a
particularly important consideration. Look for a cloud
that provides cross-platform hypervisor support and
robust instance management tools.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Application portfolio integration</term>
<listitem>
<para>An enterprise cloud delivers efficient application portfolio
management and deployments by leveraging
self-service features and rules according to use. Integrating
existing cloud environments is a common driver when building
hybrid cloud architectures.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Migration scenarios</term>
<listitem>
<para>Hybrid cloud architecture enables the migration of
applications between different clouds.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>High availability</term>
<listitem>
<para>A combination of locations and platforms enables a
level of availability that is not
possible with a single platform. This approach increases
design complexity.</para>
</listitem>
</varlistentry>
</variablelist>
<para>As running a workload on multiple cloud platforms increases design
complexity, we recommend first exploring options such as transferring
workloads across clouds at the application, instance, cloud platform,
hypervisor, and network levels.</para>
</section>
<section xml:id="tools-considerations-hybrid">
<title>Tools considerations</title>
<para>Hybrid cloud designs must incorporate tools to facilitate working
across multiple clouds.</para>
<variablelist>
<title>Tool functions</title>
<varlistentry>
<term>Broker between clouds</term>
<listitem>
<para>Brokering software evaluates relative costs between different
cloud platforms. Cloud Management Platforms (CMP)
allow the designer to determine the right location for the
workload based on predetermined criteria.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Facilitate orchestration across the clouds</term>
<listitem>
<para>CMPs simplify the migration of application workloads between
public, private, and hybrid cloud platforms. We recommend
using cloud orchestration tools for managing a diverse
portfolio of systems and applications across multiple cloud
platforms.</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="network-considerations-hybrid">
<title>Network considerations</title>
<para>It is important to consider the functionality, security, scalability,
availability, and testability of network when choosing a CMP and cloud
provider.</para>
<itemizedlist>
<listitem>
<para>Decide on a network framework and
design minimum functionality tests. This ensures
testing and functionality persists during and after
upgrades.</para>
</listitem>
<listitem>
<para>Scalability across multiple cloud providers may
dictate which underlying network framework you
choose in different cloud providers. It is important
to present the network API functions and to
verify that functionality persists across all cloud
endpoints chosen.</para>
</listitem>
<listitem>
<para>High availability implementations vary in
functionality and design. Examples of some common
methods are active-hot-standby, active-passive, and
active-active. Development of high availability and test
frameworks is necessary to insure understanding of
functionality and limitations.</para>
</listitem>
<listitem>
<para>Consider the security of data between the client and the
endpoint, and of traffic that traverses the multiple
clouds.</para>
</listitem>
</itemizedlist>
</section>
<section xml:id="risk-mitigation-management-hybrid">
<title>Risk mitigation and management considerations</title>
<para>Hybrid cloud architectures introduce additional risk because
they are more complex than a single cloud design and may involve
incompatible components or tools. However, they also reduce
risk by spreading workloads over multiple providers.</para>
<variablelist>
<title>Hybrid cloud risks</title>
<varlistentry>
<term>Provider availability or implementation details</term>
<listitem>
<para>
Business changes can affect provider availability. Likewise,
changes in a provider's service can disrupt a hybrid cloud
environment or increase costs.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Differing SLAs</term>
<listitem>
<para>Hybrid cloud designs must accommodate differences in SLAs
between providers, and consider their enforceability.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Security levels</term>
<listitem>
<para>Securing multiple cloud
environments is more complex than securing single
cloud environments. We recommend addressing concerns at
the application, network, and cloud platform levels.
Be aware that each cloud platform approaches security
differently, and a hybrid cloud design must address and
compensate for these differences.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Provider API changes</term>
<listitem>
<para>Consumers of external clouds rarely have control over
provider changes to APIs, and changes can break compatibility.
Using only the most common and basic APIs can minimize
potential conflicts.</para>
</listitem>
</varlistentry>
</variablelist>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="arch-guide-how-this-book-is-organized">
<title>How this book is organized</title>
<para>This book examines some of the most common uses for OpenStack
clouds, and explains the considerations for each use case.
Cloud architects may use this book as a comprehensive guide by
reading all of the use cases, but it is also possible to review
only the chapters which pertain to a specific use case.
The use cases covered in this guide include:</para>
<itemizedlist>
<listitem>
<para>
<link linkend="generalpurpose">General purpose</link>: Uses common components that address
80% of common use cases.
</para>
</listitem>
<listitem>
<para>
<link linkend="compute_focus">Compute focused</link>: For compute intensive workloads
such as high performance computing (HPC).
</para>
</listitem>
<listitem>
<para>
<link linkend="storage_focus">Storage focused</link>: For storage intensive workloads such as
data analytics with parallel file systems.
</para>
</listitem>
<listitem>
<para>
<link linkend="network_focus">Network focused</link>: For high performance and reliable
networking, such as a <glossterm
>content delivery network (CDN)</glossterm>.
</para>
</listitem>
<listitem>
<para>
<link linkend="multi_site">Multi-site</link>: For applications that require multiple site
deployments for geographical, reliability or data
locality reasons.
</para>
</listitem>
<listitem>
<para>
<link linkend="hybrid">Hybrid cloud</link>: Uses multiple disparate clouds
connected either for failover, hybrid cloud bursting, or
availability.
</para>
</listitem>
<listitem>
<para>
<link linkend="massively_scalable">Massively
scalable</link>: For
cloud service providers or other large
installations
</para>
</listitem>
<listitem>
<para>
<link linkend="specialized">Specialized cases</link>: Architectures that have not
previously been covered in the defined use cases.
</para>
</listitem>
</itemizedlist>
<!-- This section is currrently commented out as it is irrelevant within the current
context. However, there are plans to use this list in the future. Please do not remove.
<para>Each chapter in the guide is then further broken down into
the following sections:</para>
<itemizedlist>
<listitem>
<para>Introduction: Provides an overview of the
architectural use case.</para>
</listitem>
<listitem>
<para>User requirements: Defines the set of user
considerations that typically come into play for that
use case.</para>
</listitem>
<listitem>
<para>Technical considerations: Covers the technical
issues that must be accounted when dealing with this
use case.</para>
</listitem>
<listitem>
<para>Operational considerations: Covers the ongoing
operational tasks associated with this use case and
architecture.</para>
</listitem>
<listitem>
<para>Architecture: Covers the overall architecture
associated with the use case.</para>
</listitem>
<listitem>
<para>Prescriptive examples: Presents one or more
scenarios where this architecture could be
deployed.</para>
</listitem>
</itemizedlist>
-->
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="arch-guide-why-and-who-we-wrote-this-book">
<title>Why and how we wrote this book</title>
<para>We wrote this book to guide you through designing an OpenStack cloud
architecture. This guide identifies design considerations
for common cloud use cases and provides examples.</para>
<para>The Architecture Design Guide was written in a book sprint format,
which is a facilitated, rapid development production method for books.
The Book Sprint was facilitated by Faith Bosworth and Adam
Hyde of Book Sprints, for more information, see the Book Sprints website
(www.booksprints.net).</para>
<para>This book was written in five days during July 2014 while
exhausting the M&amp;M, Mountain Dew and healthy options
supply, complete with juggling entertainment during lunches at
VMware's headquarters in Palo Alto.</para>
<para>We would like to thank VMware for their generous
hospitality, as well as our employers, Cisco, Cloudscaling,
Comcast, EMC, Mirantis, Rackspace, Red Hat, Verizon, and
VMware, for enabling us to contribute our time. We would
especially like to thank Anne Gentle and Kenneth Hui for all
of their shepherding and organization in making this
happen.</para>
<para>The author team includes:</para>
<itemizedlist>
<listitem>
<para>Kenneth Hui (EMC)
<link xlink:href="http://twitter.com/hui_kenneth"
>@hui_kenneth</link></para>
</listitem>
<listitem>
<para>Alexandra Settle (Rackspace)
<link xlink:href="http://twitter.com/dewsday"
>@dewsday</link></para>
</listitem>
<listitem>
<para>Anthony Veiga (Comcast)
<link xlink:href="http://twitter.com/daaelar"
>@daaelar</link></para>
</listitem>
<listitem>
<para>Beth Cohen (Verizon)
<link xlink:href="http://twitter.com/bfcohen"
>@bfcohen</link></para>
</listitem>
<listitem>
<para>Kevin Jackson (Rackspace)
<link xlink:href="http://twitter.com/itarchitectkev"
>@itarchitectkev</link></para>
</listitem>
<listitem>
<para>Maish Saidel-Keesing (Cisco)
<link xlink:href="http://twitter.com/maishsk"
>@maishsk</link></para>
</listitem>
<listitem>
<para>Nick Chase (Mirantis)
<link xlink:href="http://twitter.com/NickChase"
>@NickChase</link></para>
</listitem>
<listitem>
<para>Scott Lowe (VMware)
<link xlink:href="http://twitter.com/scott_lowe"
>@scott_lowe</link></para>
</listitem>
<listitem>
<para>Sean Collins (Comcast)
<link xlink:href="http://twitter.com/sc68cal"
>@sc68cal</link></para>
</listitem>
<listitem>
<para>Sean Winn (Cloudscaling)
<link xlink:href="http://twitter.com/seanmwinn"
>@seanmwinn</link></para>
</listitem>
<listitem>
<para>Sebastian Gutierrez (Red Hat)
<link xlink:href="http://twitter.com/gutseb"
>@gutseb</link></para>
</listitem>
<listitem>
<para>Stephen Gordon (Red Hat)
<link xlink:href="http://twitter.com/xsgordon"
>@xsgordon</link></para>
</listitem>
<listitem>
<para>Vinny Valdez (Red Hat)
<link xlink:href="http://twitter.com/VinnyValdez"
>@VinnyValdez</link></para>
</listitem>
</itemizedlist>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="arch-guide-intended-audience">
<title>Intended audience</title>
<para>This book has been written for architects and designers of
OpenStack clouds. For a guide on deploying and operating
OpenStack, please refer to the <citetitle>OpenStack Operations
Guide</citetitle> (<link
xlink:href="http://docs.openstack.org/openstack-ops">http://docs.openstack.org/openstack-ops</link>).
</para>
<para>Before reading this book, we recommend prior knowledge of cloud architecture
and principles, experience in enterprise system design, Linux
and virtualization experience, and a basic understanding of
networking principles and protocols.</para>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE section [
<!ENTITY % openstack SYSTEM "../../common/entities/openstack.ent">
%openstack;
]>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="methodology">
<title>Methodology</title>
<para>The best way to design your cloud architecture is through creating and
testing use cases. Planning for applications that support thousands of
sessions per second, variable workloads, and complex, changing data,
requires you to identify the key meters. Identifying these key meters,
such as number of concurrent transactions per second, and size of
database, makes it possible to build a method for testing your assumptions.</para>
<para>Use a functional user scenario to develop test cases, and to measure
overall project trajectory.</para>
<note>
<para>If you do not want to use an application to develop user
requirements automatically, you need to create requirements to build
test harnesses and develop usable meters.</para>
</note>
<para>Establishing these meters allows you to respond to changes quickly without
having to set exact requirements in advance.
This creates ways to configure the system, rather than redesigning
it every time there is a requirements change.</para>
<important>
<para>It is important to limit scope creep. Ensure you address tool limitations,
but do not recreate the entire suite of tools. Work
with technical product owners to establish critical features that are needed
for a successful cloud deployment.</para>
</important>
<section xml:id="application-cloud-readiness-methods">
<title>Application cloud readiness</title>
<para>The cloud does more than host virtual machines and their applications.
This <emphasis>lift and shift</emphasis>
approach works in certain situations, but there is a fundamental
difference between clouds and traditional bare-metal-based
environments, or even traditional virtualized environments.</para>
<para>In traditional environments, with traditional enterprise
applications, the applications and the servers that run on them are
<emphasis>pets</emphasis>.
They are lovingly crafted and cared for, the servers have
names like Gandalf or Tardis, and if they get sick someone nurses
them back to health. All of this is designed so that the application
does not experience an outage.</para>
<para>In cloud environments, servers are more like
cattle. There are thousands of them, they get names like NY-1138-Q,
and if they get sick, they get put down and a sysadmin installs
another one. Traditional applications that are unprepared for this
kind of environment may suffer outages, loss of data, or
complete failure.</para>
<para>There are other reasons to design applications with the cloud in mind.
Some are defensive, such as the fact that because applications cannot be
certain of exactly where or on what hardware they will be launched,
they need to be flexible, or at least adaptable. Others are
proactive. For example, one of the advantages of using the cloud is
scalability. Applications need to be designed in such a way that
they can take advantage of these and other opportunities.</para>
</section>
<section xml:id="determining-whether-an-application-is-cloud-ready">
<title>Determining whether an application is cloud-ready</title>
<para>There are several factors to take into consideration when looking
at whether an application is a good fit for the cloud.</para>
<variablelist>
<varlistentry>
<term>Structure</term>
<listitem>
<para>
A large, monolithic, single-tiered, legacy
application typically is not a good fit for the
cloud. Efficiencies are gained when load can be
spread over several instances, so that a failure
in one part of the system can be mitigated without
affecting other parts of the system, or so that
scaling can take place where the app needs
it.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Dependencies</term>
<listitem>
<para>
Applications that depend on specific
hardware, such as a particular chip set or an
external device such as a fingerprint
reader, might not be a good fit for the
cloud, unless those dependencies are specifically
addressed. Similarly, if an application depends on
an operating system or set of libraries that
cannot be used in the cloud, or cannot be
virtualized, that is a problem.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Connectivity</term>
<listitem>
<para>
Self-contained applications, or those that depend
on resources that are not reachable by the cloud
in question, will not run. In some situations,
you can work around these issues with custom network
setup, but how well this works depends on the
chosen cloud environment.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Durability and resilience</term>
<listitem>
<para>
Despite the existence of SLAs, things break:
servers go down, network connections are
disrupted, or too many tenants on a server make a
server unusable. An application must be sturdy
enough to contend with these issues.
</para>
</listitem>
</varlistentry>
</variablelist>
</section>
<section xml:id="designing-for-the-cloud">
<title>Designing for the cloud</title>
<para>Here are some guidelines to keep in mind when designing an
application for the cloud:</para>
<itemizedlist>
<listitem>
<para>Be a pessimist: Assume everything fails and design
backwards.</para>
</listitem>
<listitem>
<para>Put your eggs in multiple baskets: Leverage multiple
providers, geographic regions and availability zones to
accommodate for local availability issues. Design for
portability.</para>
</listitem>
<listitem>
<para>Think efficiency: Inefficient designs will not scale.
Efficient designs become cheaper as they scale. Kill off
unneeded components or capacity.</para>
</listitem>
<listitem>
<para>Be paranoid: Design for defense in depth and zero
tolerance by building in security at every level and between
every component. Trust no one.</para>
</listitem>
<listitem>
<para>But not too paranoid: Not every application needs the
platinum solution. Architect for different SLA's, service
tiers, and security levels.</para>
</listitem>
<listitem>
<para>Manage the data: Data is usually the most inflexible and
complex area of a cloud and cloud integration architecture.
Do not short change the effort in analyzing and addressing
data needs.</para>
</listitem>
<listitem>
<para>Hands off: Leverage automation to increase consistency and
quality and reduce response times.</para>
</listitem>
<listitem>
<para>Divide and conquer: Pursue partitioning and
parallel layering wherever possible. Make components as small
and portable as possible. Use load balancing between layers.
</para>
</listitem>
<listitem>
<para>Think elasticity: Increasing resources should result in a
proportional increase in performance and scalability.
Decreasing resources should have the opposite effect.
</para>
</listitem>
<listitem>
<para>Be dynamic: Enable dynamic configuration changes such as
auto scaling, failure recovery and resource discovery to
adapt to changing environments, faults, and workload volumes.
</para>
</listitem>
<listitem>
<para>Stay close: Reduce latency by moving highly interactive
components and data near each other.</para>
</listitem>
<listitem>
<para>Keep it loose: Loose coupling, service interfaces,
separation of concerns, abstraction, and well defined API's
deliver flexibility.</para>
</listitem>
<listitem>
<para>Be cost aware: Autoscaling, data transmission, virtual
software licenses, reserved instances, and similar costs can rapidly
increase monthly usage charges. Monitor usage closely.
</para>
</listitem>
</itemizedlist>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="operational-considerations-massive-scale">
<?dbhtml stop-chunking?>
<title>Operational considerations</title>
<para>In order to run efficiently at massive scale, automate
as many of the operational processes as
possible. Automation includes the configuration of
provisioning, monitoring and alerting systems. Part of the
automation process includes the capability to determine when
human intervention is required and who should act. The
objective is to increase the ratio of operational staff to
running systems as much as possible in order to reduce maintenance
costs. In a massively scaled environment, it is very difficult
for staff to give each system individual care.</para>
<para>Configuration management tools such as Puppet and Chef enable
operations staff to categorize systems into groups based on
their roles and thus create configurations and system states
that the provisioning system enforces. Systems
that fall out of the defined state due to errors or failures
are quickly removed from the pool of active nodes and
replaced.</para>
<para>At large scale the resource cost of diagnosing failed individual
systems is far greater than the cost of
replacement. It is more economical to replace the failed
system with a new system, provisioning and configuring it
automatically and adding it to the pool of active nodes.
By automating tasks that are labor-intensive,
repetitive, and critical to operations, cloud operations
teams can work more
efficiently because fewer resources are required for these
common tasks. Administrators are then free to tackle
tasks that are not easy to automate and that have longer-term
impacts on the business, for example, capacity planning.</para>
<section xml:id="the-bleeding-edge">
<title>The bleeding edge</title>
<para>Running OpenStack at massive scale requires striking a
balance between stability and features. For example, it might
be tempting to run an older stable release branch of OpenStack
to make deployments easier. However, when running at massive
scale, known issues that may be of some concern or only have
minimal impact in smaller deployments could become pain points.
Recent releases may address well known issues. The OpenStack
community can help resolve reported issues by applying
the collective expertise of the OpenStack developers.</para>
<para>The number of organizations running at
massive scales is a small proportion of the
OpenStack community, therefore it is important to share
related issues with the community and be a vocal advocate for
resolving them. Some issues only manifest when operating at
large scale, and the number of organizations able to duplicate
and validate an issue is small, so it is important to
document and dedicate resources to their resolution.</para>
<para>In some cases, the resolution to the problem is ultimately
to deploy a more recent version of OpenStack. Alternatively,
when you must resolve an issue in a production
environment where rebuilding the entire environment is not an
option, it is sometimes possible to deploy updates to specific
underlying components in order to resolve issues or gain
significant performance improvements. Although this may appear
to expose the deployment to
increased risk and instability, in many cases it
could be an undiscovered issue.</para>
<para>We recommend building a development and operations
organization that is responsible for creating desired
features, diagnosing and resolving issues, and building the
infrastructure for large scale continuous integration tests
and continuous deployment. This helps catch bugs early and
makes deployments faster and easier. In addition to
development resources, we also recommend the recruitment
of experts in the fields of message queues, databases, distributed
systems, networking, cloud, and storage.</para></section>
<section xml:id="growth-and-capacity-planning">
<title>Growth and capacity planning</title>
<para>An important consideration in running at massive scale is
projecting growth and utilization trends in order to plan capital
expenditures for the short and long term. Gather utilization
meters for compute, network, and storage, along with historical
records of these meters. While securing major
anchor tenants can lead to rapid jumps in the utilization
rates of all resources, the steady adoption of the cloud
inside an organization or by consumers in a public
offering also creates a steady trend of increased
utilization.</para></section>
<section xml:id="skills-and-training">
<title>Skills and training</title>
<para>Projecting growth for storage, networking, and compute is
only one aspect of a growth plan for running OpenStack at
massive scale. Growing and nurturing development and
operational staff is an additional consideration. Sending team
members to OpenStack conferences, meetup events, and
encouraging active participation in the mailing lists and
committees is a very important way to maintain skills and
forge relationships in the community. For a list of OpenStack
training providers in the marketplace, see: <link
xlink:href="http://www.openstack.org/marketplace/training/">http://www.openstack.org/marketplace/training/</link>.
</para>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE section [
<!ENTITY % openstack SYSTEM "../../common/entities/openstack.ent">
%openstack;
]>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="technical-considerations-massive-scale">
<?dbhtml stop-chunking?>
<title>Technical considerations</title>
<para>Repurposing an existing OpenStack environment to be
massively scalable is a formidable task. When building
a massively scalable environment from the ground up, ensure
you build the initial deployment with the same principles
and choices that apply as the environment grows. For example,
a good approach is to deploy the first site as a multi-site
environment. This enables you to use the same deployment
and segregation methods as the environment grows to separate
locations across dedicated links or wide area networks. In
a hyperscale cloud, scale trumps redundancy. Modify applications
with this in mind, relying on the scale and homogeneity of the
environment to provide reliability rather than redundant
infrastructure provided by non-commodity hardware
solutions.</para>
<section xml:id="infrastructure-segregation-massive-scale">
<title>Infrastructure segregation</title>
<para>OpenStack services support massive horizontal scale.
Be aware that this is not the case for the entire supporting
infrastructure. This is particularly a problem for the database
management systems and message queues that OpenStack services
use for data storage and remote procedure call communications.</para>
<para>Traditional clustering techniques typically
provide high availability and some additional scale for these
environments. In the quest for massive scale, however, you must
take additional steps to relieve the performance
pressure on these components in order to prevent them from negatively
impacting the overall performance of the environment. Ensure that
all the components are in balance so that if the massively
scalable environment fails, all the components are near maximum
capacity and a single component is not causing the failure.</para>
<para>Regions segregate completely independent
installations linked only by an Identity and Dashboard
(optional) installation. Services have separate
API endpoints for each region, and include separate database
and queue installations. This exposes some awareness of the
environment's fault domains to users and gives them the
ability to ensure some degree of application resiliency while
also imposing the requirement to specify which region to apply
their actions to.</para>
<para>Environments operating at massive scale typically need their
regions or sites subdivided further without exposing the
requirement to specify the failure domain to the user. This
provides the ability to further divide the installation into
failure domains while also providing a logical unit for
maintenance and the addition of new hardware. At hyperscale,
instead of adding single compute nodes, administrators can add
entire racks or even groups of racks at a time with each new
addition of nodes exposed via one of the segregation concepts
mentioned herein.</para>
<para><glossterm baseform="cell">Cells</glossterm> provide the ability
to subdivide the compute portion
of an OpenStack installation, including regions, while still
exposing a single endpoint. Each region has an API cell
along with a number of compute cells where the
workloads actually run. Each cell has its own database and
message queue setup (ideally clustered), providing the ability
to subdivide the load on these subsystems, improving overall
performance.</para>
<para>Each compute cell provides a complete compute installation,
complete with full database and queue installations,
scheduler, conductor, and multiple compute hosts. The cells
scheduler handles placement of user requests from the single
API endpoint to a specific cell from those available. The
normal filter scheduler then handles placement within the
cell.</para>
<para>Unfortunately, Compute is the only OpenStack service that
provides good support for cells. In addition, cells
do not adequately support some standard
OpenStack functionality such as security groups and host
aggregates. Due to their relative newness and specialized use,
cells receive relatively little testing in the OpenStack gate.
Despite these issues, cells play an important role in
well known OpenStack installations operating at massive scale,
such as those at CERN and Rackspace.</para></section>
<section xml:id="host-aggregates">
<title>Host aggregates</title>
<para>Host aggregates enable partitioning of OpenStack Compute
deployments into logical groups for load balancing and
instance distribution. You can also use host aggregates to
further partition an availability zone. Consider a cloud which
might use host aggregates to partition an availability zone
into groups of hosts that either share common resources, such
as storage and network, or have a special property, such as
trusted computing hardware. You cannot target host aggregates
explicitly. Instead, select instance flavors that map to host
aggregate metadata. These flavors target host aggregates
implicitly.</para></section>
<section xml:id="availability-zones">
<title>Availability zones</title>
<para>Availability zones provide another mechanism for subdividing
an installation or region. They are, in effect, host
aggregates exposed for (optional) explicit targeting
by users.</para>
<para>Unlike cells, availability zones do not have their own database
server or queue broker but represent an arbitrary grouping of
compute nodes. Typically, nodes are grouped into availability
zones using a shared failure domain based on a physical
characteristic such as a shared power source or physical network
connections. Users can target exposed availability zones; however,
this is not a requirement. An alternative approach is to set a default
availability zone to schedule instances to a non-default availability
zone of <literal>nova</literal>.</para></section>
<section xml:id="segregation-example">
<title>Segregation example</title>
<para>In this example the cloud is divided into two regions, one
for each site, with two availability zones in each based on
the power layout of the data centers. A number of host
aggregates enable targeting of
virtual machine instances using flavors, that require special
capabilities shared by the target hosts such as SSDs, 10&nbsp;GbE
networks, or GPU cards.</para>
<mediaobject>
<imageobject>
<imagedata contentwidth="4in"
fileref="../figures/Massively_Scalable_Cells_+_regions_+_azs.png"
/>
</imageobject>
</mediaobject></section>
</section>

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<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="user-requirements-massive-scale-overview">
<?dbhtml stop-chunking?>
<title>User requirements</title>
<para>Defining user requirements for a massively scalable OpenStack
design architecture dictates approaching the design from two
different, yet sometimes opposing, perspectives: the cloud
user, and the cloud operator. The expectations and perceptions
of the consumption and management of resources of a massively
scalable OpenStack cloud from these two perspectives are
distinctly different.</para>
<para>Massively scalable OpenStack clouds have the following user
requirements:</para>
<itemizedlist>
<listitem>
<para>The cloud user expects repeatable, dependable, and
deterministic processes for launching and deploying
cloud resources. You could deliver this through a
web-based interface or publicly available API
endpoints. All appropriate options for requesting
cloud resources must be available through some type
of user interface, a command-line interface (CLI), or
API endpoints.</para>
</listitem>
<listitem>
<para>Cloud users expect a fully self-service and
on-demand consumption model. When an OpenStack cloud
reaches the "massively scalable" size, expect
consumption "as a service" in each and
every way.</para>
</listitem>
<listitem>
<para>For a user of a massively scalable OpenStack public
cloud, there are no expectations for control over
security, performance, or availability. Users expect
only SLAs related to uptime of API services, and
very basic SLAs for services offered. It is the user's
responsibility to address these issues on their own.
The exception to this expectation is the rare case of
a massively scalable cloud infrastructure built for
a private or government organization that has
specific requirements.</para>
</listitem>
</itemizedlist>
<para>The cloud user's requirements and expectations that determine
the cloud design focus on the consumption model. The user
expects to consume cloud resources in an automated and
deterministic way, without any need for knowledge of the
capacity, scalability, or other attributes of the cloud's
underlying infrastructure.</para>
<section xml:id="operator-requirements-massive-scale">
<title>Operator requirements</title>
<para>While the cloud user can be completely unaware of the
underlying infrastructure of the cloud and its attributes, the
operator must build and support the infrastructure for operating
at scale. This presents a very demanding set of requirements
for building such a cloud from the operator's perspective:</para>
<itemizedlist>
<listitem>
<para>Everything must be capable of automation. For example,
everything from compute hardware, storage hardware,
networking hardware, to the installation and
configuration of the supporting software. Manual
processes are impractical in a massively scalable
OpenStack design architecture.</para>
</listitem>
<listitem>
<para>The cloud operator requires that capital expenditure
(CapEx) is minimized at all layers of the stack.
Operators of massively scalable OpenStack clouds
require the use of dependable commodity hardware and
freely available open source software components to
reduce deployment costs and operational expenses.
Initiatives like OpenCompute (more information
available at <link
xlink:href="http://www.opencompute.org">http://www.opencompute.org</link>)
provide additional information and pointers. To cut
costs, many operators sacrifice redundancy. For
example, using redundant power supplies, network
connections, and rack switches.</para>
</listitem>
<listitem>
<para>Companies operating a massively scalable OpenStack
cloud also require that operational expenditures
(OpEx) be minimized as much as possible. We
recommend using cloud-optimized hardware when
managing operational overhead. Some of
the factors to consider include power,
cooling, and the physical design of the chassis. Through
customization, it is possible to optimize the hardware
and systems for this type of workload because of the
scale of these implementations.</para>
</listitem>
<listitem>
<para>Massively scalable OpenStack clouds require
extensive metering and monitoring functionality to
maximize the operational efficiency by keeping the
operator informed about the status and state of the
infrastructure. This includes full scale metering of
the hardware and software status. A corresponding
framework of logging and alerting is also required to
store and enable operations to act on the meters
provided by the metering and monitoring solutions.
The cloud operator also needs a solution that uses the
data provided by the metering and monitoring solution
to provide capacity planning and capacity trending
analysis.</para>
</listitem>
<listitem>
<para>Invariably, massively scalable OpenStack clouds extend
over several sites. Therefore, the user-operator
requirements for a multi-site OpenStack architecture
design are also applicable here. This includes various
legal requirements; other jurisdictional legal or
compliance requirements; image
consistency-availability; storage replication and
availability (both block and file/object storage); and
authentication, authorization, and auditing (AAA).
See <xref linkend="multi_site"/>
for more details on requirements and considerations
for multi-site OpenStack clouds.</para>
</listitem>
<listitem>
<para>The design architecture of a massively scalable OpenStack
cloud must address considerations around physical
facilities such as space, floor weight, rack height and
type, environmental considerations, power usage and power
usage efficiency (PUE), and physical security.</para>
</listitem>
</itemizedlist></section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="arch-design-architecture-multiple-site">
<?dbhtml stop-chunking?>
<title>Architecture</title>
<para><xref linkend="multi-site_arch"/>
illustrates a high level multi-site OpenStack
architecture. Each site is an OpenStack cloud but it may be necessary
to architect the sites on different versions. For example, if the
second site is intended to be a replacement for the first site,
they would be different. Another common design would be a private
OpenStack cloud with a replicated site that would be used for high
availability or disaster recovery. The most important design decision
is configuring storage as a single shared pool or separate pools,
depending on user and technical requirements.</para>
<figure xml:id="multi-site_arch">
<title>Multi-site OpenStack architecture</title>
<mediaobject>
<imageobject>
<imagedata contentwidth="6in"
fileref="../figures/Multi-Site_shared_keystone_horizon_swift1.png"/>
</imageobject>
</mediaobject>
</figure>
<section xml:id="openstack-services-architecture">
<title>OpenStack services architecture</title>
<para>The Identity service, which is used by all other
OpenStack components for authorization and the catalog of
service endpoints, supports the concept of regions. A region
is a logical construct used to group OpenStack services in
close proximity to one another. The concept of
regions is flexible; it may contain OpenStack service
endpoints located within a distinct geographic region or regions.
It may be smaller in scope, where a region is a single rack
within a data center, with multiple regions existing in adjacent
racks in the same data center.</para>
<para>The majority of OpenStack components are designed to run
within the context of a single region. The Compute
service is designed to manage compute resources within a region,
with support for subdivisions of compute resources by using
availability zones and cells. The Networking service
can be used to manage network resources in the same broadcast
domain or collection of switches that are linked. The OpenStack
Block Storage service controls storage resources within a region
with all storage resources residing on the same storage network.
Like the OpenStack Compute service, the OpenStack Block Storage
service also supports the availability zone construct which can
be used to subdivide storage resources.</para>
<para>The OpenStack dashboard, OpenStack Identity, and OpenStack
Object Storage services are components that can each be deployed
centrally in order to serve multiple regions.</para>
</section>
<section xml:id="arch-multi-storage">
<title>Storage</title>
<para>With multiple OpenStack regions, it is recommended to configure
a single OpenStack Object Storage service endpoint to deliver
shared file storage for all regions. The Object Storage service
internally replicates files to multiple nodes which can be used
by applications or workloads in multiple regions. This simplifies
high availability failover and disaster recovery rollback.</para>
<para>In order to scale the Object Storage service to meet the workload
of multiple regions, multiple proxy workers are run and
load-balanced, storage nodes are installed in each region, and the
entire Object Storage Service can be fronted by an HTTP caching
layer. This is done so client requests for objects can be served out
of caches rather than directly from the storage modules themselves,
reducing the actual load on the storage network. In addition to an
HTTP caching layer, use a caching layer like Memcache to cache
objects between the proxy and storage nodes.</para>
<para>If the cloud is designed with a separate Object Storage
service endpoint made available in each region, applications are
required to handle synchronization (if desired) and other management
operations to ensure consistency across the nodes. For some
applications, having multiple Object Storage Service endpoints
located in the same region as the application may be desirable due
to reduced latency, cross region bandwidth, and ease of
deployment.</para>
<note>
<para>For the Block Storage service, the most important decisions
are the selection of the storage technology, and whether
a dedicated network is used to carry storage traffic
from the storage service to the compute nodes.</para>
</note>
</section>
<section xml:id="arch-networking-multiple">
<title>Networking</title>
<para>When connecting multiple regions together, there are several design
considerations. The overlay network technology choice determines how
packets are transmitted between regions and how the logical network
and addresses present to the application. If there are security or
regulatory requirements, encryption should be implemented to secure
the traffic between regions. For networking inside a region, the
overlay network technology for tenant networks is equally important.
The overlay technology and the network traffic that an application
generates or receives can be either complementary or serve cross
purposes. For example, using an overlay technology for an application
that transmits a large amount of small packets could add excessive
latency or overhead to each packet if not configured
properly.</para>
</section>
<section xml:id="arch-dependencies-multiple">
<title>Dependencies</title>
<para>The architecture for a multi-site OpenStack installation
is dependent on a number of factors. One major dependency to
consider is storage. When designing the storage system, the
storage mechanism needs to be determined. Once the storage
type is determined, how it is accessed is critical. For example,
we recommend that storage should use a dedicated network.
Another concern is how the storage is configured to protect
the data. For example, the Recovery Point Objective (RPO) and
the Recovery Time Objective (RTO). How quickly recovery from
a fault can be completed, determines how often the replication of
data is required. Ensure that enough storage is allocated to
support the data protection strategy.
</para>
<para>Networking decisions include the encapsulation mechanism that can
be used for the tenant networks, how large the broadcast domains
should be, and the contracted SLAs for the interconnects.</para>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="operational-considerations-multi-site">
<?dbhtml stop-chunking?>
<title>Operational considerations</title>
<para>Multi-site OpenStack cloud deployment using regions
requires that the service catalog contains per-region entries
for each service deployed other than the Identity service. Most
off-the-shelf OpenStack deployment tools have limited support
for defining multiple regions in this fashion.</para>
<para>Deployers should be aware of this and provide the appropriate
customization of the service catalog for their site either
manually, or by customizing deployment tools in use.</para>
<note><para>As of the Kilo release, documentation for
implementing this feature is in progress. See this bug for
more information:
<link
xlink:href="https://bugs.launchpad.net/openstack-manuals/+bug/1340509">https://bugs.launchpad.net/openstack-manuals/+bug/1340509</link>.
</para></note>
<section xml:id="licensing">
<title>Licensing</title>
<para>Multi-site OpenStack deployments present additional
licensing considerations over and above regular OpenStack
clouds, particularly where site licenses are in use to provide
cost efficient access to software licenses. The licensing for
host operating systems, guest operating systems, OpenStack
distributions (if applicable), software-defined infrastructure
including network controllers and storage systems, and even
individual applications need to be evaluated.</para>
<para>Topics to consider include:</para>
<itemizedlist>
<listitem>
<para>The definition of what constitutes a site
in the relevant licenses, as the term does not
necessarily denote a geographic or otherwise
physically isolated location.</para>
</listitem>
<listitem>
<para>Differentiations between "hot" (active) and "cold"
(inactive) sites, where significant savings may be made
in situations where one site is a cold standby for
disaster recovery purposes only.</para>
</listitem>
<listitem>
<para>Certain locations might require local vendors to
provide support and services for each site which may vary
with the licensing agreement in place.</para>
</listitem>
</itemizedlist></section>
<section xml:id="logging-and-monitoring-multi-site">
<title>Logging and monitoring</title>
<para>Logging and monitoring does not significantly differ for a
multi-site OpenStack cloud. The tools described in the <link
xlink:href="http://docs.openstack.org/openstack-ops/content/logging_monitoring.html">Logging
and monitoring chapter</link> of the <citetitle>Operations
Guide</citetitle> remain applicable. Logging and monitoring
can be provided on a per-site basis, and in a common
centralized location.</para>
<para>When attempting to deploy logging and monitoring facilities
to a centralized location, care must be taken with the load
placed on the inter-site networking links.</para></section>
<section xml:id="upgrades-multi-site">
<title>Upgrades</title>
<para>In multi-site OpenStack clouds deployed using regions, sites
are independent OpenStack installations which are linked
together using shared centralized services such as OpenStack
Identity. At a high level the recommended order of operations
to upgrade an individual OpenStack environment is (see the <link
xlink:href="http://docs.openstack.org/openstack-ops/content/ops_upgrades-general-steps.html">Upgrades
chapter</link> of the <citetitle>Operations Guide</citetitle>
for details):</para>
<orderedlist>
<listitem>
<para>Upgrade the OpenStack Identity service
(keystone).</para>
</listitem>
<listitem>
<para>Upgrade the OpenStack Image service (glance).</para>
</listitem>
<listitem>
<para>Upgrade OpenStack Compute (nova), including
networking components.</para>
</listitem>
<listitem>
<para>Upgrade OpenStack Block Storage (cinder).</para>
</listitem>
<listitem>
<para>Upgrade the OpenStack dashboard (horizon).</para>
</listitem>
</orderedlist>
<para>The process for upgrading a multi-site environment is not
significantly different:</para>
<orderedlist>
<listitem>
<para>Upgrade the shared OpenStack Identity service
(keystone) deployment.</para>
</listitem>
<listitem>
<para>Upgrade the OpenStack Image service (glance) at each
site.</para>
</listitem>
<listitem>
<para>Upgrade OpenStack Compute (nova), including
networking components, at each site.</para>
</listitem>
<listitem>
<para>Upgrade OpenStack Block Storage (cinder) at each
site.</para>
</listitem>
<listitem>
<para>Upgrade the OpenStack dashboard (horizon), at each
site or in the single central location if it is
shared.</para>
</listitem>
</orderedlist>
<para>Compute upgrades within each site can also be performed in a rolling
fashion. Compute controller services (API, Scheduler, and
Conductor) can be upgraded prior to upgrading of individual
compute nodes. This allows operations staff to keep a site
operational for users of Compute services while performing an
upgrade.</para></section>
<section xml:id="quota-management-multi-site">
<title>Quota management</title>
<para>Quotas are used to set operational limits to prevent system
capacities from being exhausted without notification. They are
currently enforced at the tenant (or project) level rather than
at the user level.</para>
<para>Quotas are defined on a per-region basis. Operators can
define identical quotas for tenants in each region of the
cloud to provide a consistent experience, or even create a
process for synchronizing allocated quotas across regions. It
is important to note that only the operational limits imposed
by the quotas will be aligned consumption of quotas by users
will not be reflected between regions.</para>
<para>For example, given a cloud with two regions, if the operator
grants a user a quota of 25 instances in each region then that
user may launch a total of 50 instances spread across both
regions. They may not, however, launch more than 25 instances
in any single region.</para>
<para>For more information on managing quotas refer to the
<link
xlink:href="http://docs.openstack.org/openstack-ops/content/projects_users.html">Managing
projects and users chapter</link> of the <citetitle>OpenStack
Operators Guide</citetitle>.</para>
</section>
<section xml:id="policy-management-multi-site">
<title>Policy management</title>
<para>OpenStack provides a default set of Role Based Access
Control (RBAC) policies, defined in a <filename>policy.json</filename> file, for
each service. Operators edit these files to customize the
policies for their OpenStack installation. If the application
of consistent RBAC policies across sites is a requirement, then
it is necessary to ensure proper synchronization of the
<filename>policy.json</filename> files to all installations.</para>
<para>This must be done using system administration tools
such as rsync as functionality for synchronizing policies
across regions is not currently provided within OpenStack.</para></section>
<section xml:id="documentation-multi-site">
<title>Documentation</title>
<para>Users must be able to leverage cloud infrastructure and
provision new resources in the environment. It is important
that user documentation is accessible by users to ensure they
are given sufficient information to help them leverage the cloud.
As an example, by default OpenStack schedules instances on a compute node
automatically. However, when multiple regions are available,
the end user needs to decide in which region to schedule the
new instance. The dashboard presents the user with
the first region in your configuration. The API and CLI tools
do not execute commands unless a valid region is specified.
It is therefore important to provide documentation to your
users describing the region layout as well as calling out that
quotas are region-specific. If a user reaches his or her quota
in one region, OpenStack does not automatically build new
instances in another. Documenting specific examples helps
users understand how to operate the cloud, thereby reducing
calls and tickets filed with the help desk.</para></section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE section [
<!ENTITY % openstack SYSTEM "../../common/entities/openstack.ent">
%openstack;
]>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="prescriptive-example-multisite">
<?dbhtml stop-chunking?>
<title>Prescriptive examples</title>
<para>There are multiple ways to build a multi-site OpenStack
installation, based on the needs of the intended workloads.
Below are example architectures based on different
requirements. These examples are meant as a reference, and not
a hard and fast rule for deployments. Use the previous
sections of this chapter to assist in selecting specific
components and implementations based on specific needs.</para>
<para>A large content provider needs to deliver content to
customers that are geographically dispersed. The workload is
very sensitive to latency and needs a rapid response to
end-users. After reviewing the user, technical and operational
considerations, it is determined beneficial to build a number
of regions local to the customer's edge. Rather than build a
few large, centralized data centers, the intent of the architecture
is to provide a pair of small data centers in locations that
are closer to the customer. In this use
case, spreading applications out allows for different
horizontal scaling than a traditional compute workload scale.
The intent is to scale by creating more copies of the
application in closer proximity to the users that need it
most, in order to ensure faster response time to user
requests. This provider deploys two datacenters at each of
the four chosen regions. The implications of this design are
based around the method of placing copies of resources in each
of the remote regions. Swift objects, Glance images, and block
storage need to be manually replicated into each region.
This may be beneficial for some systems, such as the case of
content service, where only some of the content needs to exist
in some but not all regions. A centralized Keystone is
recommended to ensure authentication and that access to the
API endpoints is easily manageable.</para>
<para>It is recommended that you install an automated DNS system such
as Designate. Application administrators need a way to
manage the mapping of which application copy exists in each
region and how to reach it, unless an external Dynamic DNS system
is available. Designate assists by making the process automatic
and by populating the records in the each region's zone.</para>
<para>Telemetry for each region is also deployed, as each region
may grow differently or be used at a different rate.
Ceilometer collects each region's meters from each
of the controllers and report them back to a central location.
This is useful both to the end user and the administrator of
the OpenStack environment. The end user will find this method
useful, as it makes possible to determine if certain
locations are experiencing higher load than others, and take
appropriate action. Administrators also benefit by
possibly being able to forecast growth per region, rather than
expanding the capacity of all regions simultaneously,
therefore maximizing the cost-effectiveness of the multi-site
design.</para>
<para>One of the key decisions of running this infrastructure is
whether or not to provide a redundancy
model. Two types of redundancy and high availability models in
this configuration can be implemented. The first type
is the availability of central OpenStack
components. Keystone can be made highly available in three
central data centers that host the centralized OpenStack
components. This prevents a loss of any one of the regions
causing an outage in service. It also has the added benefit of
being able to run a central storage repository as a primary
cache for distributing content to each of the regions.</para>
<para>The second redundancy type is the edge data center itself.
A second data center in each of the edge regional
locations house a second region near the first region. This
ensures that the application does not suffer degraded
performance in terms of latency and availability.</para>
<para><xref linkend="multi-site_customer_edge"/> depicts
the solution designed to have both a centralized set of core
data centers for OpenStack services and paired edge data centers:</para>
<figure xml:id="multi-site_customer_edge">
<title>Multi-site architecture example</title>
<mediaobject>
<imageobject>
<imagedata contentwidth="6in"
fileref="../figures/Multi-Site_Customer_Edge.png"/>
</imageobject>
</mediaobject>
</figure>
<section xml:id="geo-redundant-load-balancing">
<title>Geo-redundant load balancing</title>
<para>A large-scale web application has been designed with cloud
principles in mind. The application is designed provide
service to application store, on a 24/7 basis. The company has
typical two tier architecture with a web front-end servicing the
customer requests, and a NoSQL database back end storing the
information.</para>
<para>As of late there has been several outages in number of major
public cloud providers due to applications running out of
a single geographical location. The design therefore should
mitigate the chance of a single site causing an outage for their
business.</para>
<para>The solution would consist of the following OpenStack
components:</para>
<itemizedlist>
<listitem>
<para>A firewall, switches and load balancers on the
public facing network connections.</para>
</listitem>
<listitem>
<para>OpenStack Controller services running, Networking,
dashboard, Block Storage and Compute running locally in
each of the three regions. Identity service, Orchestration
service, Telemetry service, Image service and
Object Storage service can be installed centrally, with
nodes in each of the region providing a redundant
OpenStack Controller plane throughout the globe.</para>
</listitem>
<listitem>
<para>OpenStack Compute nodes running the KVM
hypervisor.</para>
</listitem>
<listitem>
<para>OpenStack Object Storage for serving static objects
such as images can be used to ensure that all images
are standardized across all the regions, and
replicated on a regular basis.</para>
</listitem>
<listitem>
<para>A distributed DNS service available to all
regions that allows for dynamic update of DNS
records of deployed instances.</para>
</listitem>
<listitem>
<para>A geo-redundant load balancing service can be used
to service the requests from the customers based on
their origin.</para>
</listitem>
</itemizedlist>
<para>An autoscaling heat template can be used to deploy the
application in the three regions. This template includes:</para>
<itemizedlist>
<listitem>
<para>Web Servers, running Apache.</para>
</listitem>
<listitem>
<para>Appropriate <literal>user_data</literal> to populate the central DNS
servers upon instance launch.</para>
</listitem>
<listitem>
<para>Appropriate Telemetry alarms that maintain state of
the application and allow for handling of region or
instance failure.</para>
</listitem>
</itemizedlist>
<para>Another autoscaling Heat template can be used to deploy a
distributed MongoDB shard over the three locations, with the
option of storing required data on a globally available swift
container. According to the usage and load on the database
server, additional shards can be provisioned according to
the thresholds defined in Telemetry.</para>
<!-- <para>The reason that three regions were selected here was because of
the fear of having abnormal load on a single region in the
event of a failure. Two data center would have been sufficient
had the requirements been met.</para>-->
<para>Two data centers would have been sufficient had the requirements
been met. But three regions are selected here to avoid abnormal
load on a single region in the event of a failure.</para>
<para>Orchestration is used because of the built-in functionality of
autoscaling and auto healing in the event of increased load.
Additional configuration management tools, such as Puppet or
Chef could also have been used in this scenario, but were not
chosen since Orchestration had the appropriate built-in
hooks into the OpenStack cloud, whereas the other tools were
external and not native to OpenStack. In addition, external
tools were not needed since this deployment scenario was straight
forward.</para>
<para>OpenStack Object Storage is used here to serve as a back end for
the Image service since it is the most suitable solution for a
globally distributed storage solution with its own
replication mechanism. Home grown solutions could also have
been used including the handling of replication, but were not
chosen, because Object Storage is already an intricate part of the
infrastructure and a proven solution.</para>
<para>An external load balancing service was used and not the
LBaaS in OpenStack because the solution in OpenStack is not
redundant and does not have any awareness of geo location.</para>
<figure xml:id="multi-site_geo_redundant">
<title>Multi-site geo-redundant architecture</title>
<mediaobject>
<imageobject>
<imagedata contentwidth="6in"
fileref="../figures/Multi-site_Geo_Redundant_LB.png"/>
</imageobject>
</mediaobject>
</figure>
</section>
<section xml:id="location-local-services">
<title>Location-local service</title>
<para>A common use for multi-site OpenStack deployment is
creating a Content Delivery Network. An application that
uses a location-local architecture requires low network
latency and proximity to the user to provide an
optimal user experience and reduce the cost of bandwidth and
transit. The content resides on sites closer to the customer,
instead of a centralized content store that requires utilizing
higher cost cross-country links.</para>
<para>This architecture includes a geo-location component
that places user requests to the closest possible node. In
this scenario, 100% redundancy of content across every site is
a goal rather than a requirement, with the intent to
maximize the amount of content available within a
minimum number of network hops for end users. Despite
these differences, the storage replication configuration has
significant overlap with that of a geo-redundant load
balancing use case.</para>
<para>In <xref linkend="multi-site_shared_shared_keystone"/>,
the application utilizing this multi-site OpenStack install
that is location-aware would launch web server or content
serving instances on the compute cluster in each site. Requests
from clients are first sent to a global services load balancer
that determines the location of the client, then routes the
request to the closest OpenStack site where the application
completes the request.</para>
<figure xml:id="multi-site_shared_shared_keystone">
<title>Multi-site shared keystone architecture</title>
<mediaobject>
<imageobject>
<imagedata contentwidth="6in"
fileref="../figures/Multi-Site_shared_keystone1.png"/>
</imageobject>
</mediaobject>
</figure>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="technical-considerations-multi-site">
<?dbhtml stop-chunking?>
<title>Technical considerations</title>
<para>There are many technical considerations to take into account
with regard to designing a multi-site OpenStack
implementation. An OpenStack cloud can be designed in a
variety of ways to handle individual application needs. A
multi-site deployment has additional challenges compared
to single site installations and therefore is a more
complex solution.</para>
<para>When determining capacity options be sure to take into
account not just the technical issues, but also the economic
or operational issues that might arise from specific
decisions.</para>
<para>Inter-site link capacity describes the capabilities of the
connectivity between the different OpenStack sites. This
includes parameters such as bandwidth, latency, whether or not
a link is dedicated, and any business policies applied to the
connection. The capability and number of the links between
sites determine what kind of options are available for
deployment. For example, if two sites have a pair of
high-bandwidth links available between them, it may be wise to
configure a separate storage replication network between the
two sites to support a single Swift endpoint and a shared
Object Storage capability between them. An example of this
technique, as well as a configuration walk-through, is
available at <link
xlink:href="http://docs.openstack.org/developer/swift/replication_network.html#dedicated-replication-network">http://docs.openstack.org/developer/swift/replication_network.html#dedicated-replication-network</link>.
Another option in this scenario is to build a dedicated set of
tenant private networks across the secondary link, using
overlay networks with a third party mapping the site overlays
to each other.</para>
<para>The capacity requirements of the links between sites is
driven by application behavior. If the link latency is
too high, certain applications that use a large number of
small packets, for example RPC calls, may encounter issues
communicating with each other or operating properly.
Additionally, OpenStack may encounter similar types of issues.
To mitigate this, Identity service call timeouts can be
tuned to prevent issues authenticating against a central
Identity service.</para>
<para>Another network capacity consideration for a multi-site
deployment is the amount and performance of overlay networks
available for tenant networks. If using shared tenant networks
across zones, it is imperative that an external overlay manager
or controller be used to map these overlays together. It is
necessary to ensure the amount of possible IDs between the zones
are identical.</para>
<note>
<para>As of the Kilo release, OpenStack Networking was not
capable of managing tunnel IDs across installations. So if
one site runs out of IDs, but another does not, that tenant's
network is unable to reach the other site.</para>
</note>
<para>Capacity can take other forms as well. The ability for a
region to grow depends on scaling out the number of available
compute nodes. This topic is covered in greater detail in the
section for compute-focused deployments. However, it may be
necessary to grow cells in an individual region, depending on
the size of your cluster and the ratio of virtual machines per
hypervisor.</para>
<para>A third form of capacity comes in the multi-region-capable
components of OpenStack. Centralized Object Storage is capable
of serving objects through a single namespace across multiple
regions. Since this works by accessing the object store through
swift proxy, it is possible to overload the proxies. There are
two options available to mitigate this issue:</para>
<itemizedlist>
<listitem>
<para>Deploy a large number of swift proxies. The drawback is
that the proxies are not load-balanced and a large file
request could continually hit the same proxy.</para>
</listitem>
<listitem>
<para>Add a caching HTTP proxy and load balancer in front of
the swift proxies. Since swift objects are returned to the
requester via HTTP, this load balancer would alleviate the
load required on the swift proxies.</para>
</listitem>
</itemizedlist>
<section xml:id="utilization-multi-site"><title>Utilization</title>
<para>While constructing a multi-site OpenStack environment is the
goal of this guide, the real test is whether an application
can utilize it.</para>
<para>The Identity service is normally the first interface for
OpenStack users and is required for almost all major operations
within OpenStack. Therefore, it is important that you provide users
with a single URL for Identity service authentication, and
document the configuration of regions within the Identity service.
Each of the sites defined in your installation is considered
to be a region in Identity nomenclature. This is important for
the users, as it is required to define the region name when
providing actions to an API endpoint or in the dashboard.</para>
<para>Load balancing is another common issue with multi-site
installations. While it is still possible to run HAproxy
instances with Load-Balancer-as-a-Service, these are defined
to a specific region. Some applications can manage this using
internal mechanisms. Other applications may require the
implementation of an external system, including global services
load balancers or anycast-advertised DNS.</para>
<para>Depending on the storage model chosen during site design,
storage replication and availability are also a concern
for end-users. If an application can support regions, then it
is possible to keep the object storage system separated by region.
In this case, users who want to have an object available to
more than one region need to perform cross-site replication.
However, with a centralized swift proxy, the user may need to
benchmark the replication timing of the Object Storage back end.
Benchmarking allows the operational staff to provide users with
an understanding of the amount of time required for a stored or
modified object to become available to the entire environment.</para>
</section>
<section xml:id="performance"><title>Performance</title>
<para>Determining the performance of a multi-site installation
involves considerations that do not come into play in a
single-site deployment. Being a distributed deployment,
performance in multi-site deployments may be affected in certain
situations.</para>
<para>Since multi-site systems can be geographically separated,
there may be greater latency or jitter when communicating across
regions. This can especially impact systems like the OpenStack
Identity service when making authentication attempts from regions
that do not contain the centralized Identity implementation. It
can also affect applications which rely on Remote Procedure Call (RPC)
for normal operation. An example of this can be seen in high
performance computing workloads.</para>
<para>Storage availability can also be impacted by the
architecture of a multi-site deployment. A centralized Object
Storage service requires more time for an object to be
available to instances locally in regions where the object was
not created. Some applications may need to be tuned to account
for this effect. Block Storage does not currently have a
method for replicating data across multiple regions, so
applications that depend on available block storage need
to manually cope with this limitation by creating duplicate
block storage entries in each region.</para>
</section>
<section xml:id="openstack-components_multi-site">
<title>OpenStack components</title>
<para>Most OpenStack installations require a bare minimum set of
pieces to function. These include the OpenStack Identity
(keystone) for authentication, OpenStack Compute
(nova) for compute, OpenStack Image service (glance) for image
storage, OpenStack Networking (neutron) for networking, and
potentially an object store in the form of OpenStack Object
Storage (swift). Deploying a multi-site installation also demands extra
components in order to coordinate between regions. A centralized
Identity service is necessary to provide the single authentication
point. A centralized dashboard is also recommended to provide a
single login point and a mapping to the API and CLI
options available. A centralized Object Storage service may also
be used, but will require the installation of the swift proxy
service.</para>
<para>It may also be helpful to install a few extra options in
order to facilitate certain use cases. For example,
installing Designate may assist in automatically generating
DNS domains for each region with an automatically-populated
zone full of resource records for each instance. This
facilitates using DNS as a mechanism for determining which
region will be selected for certain applications.</para>
<para>Another useful tool for managing a multi-site installation
is Orchestration (heat). The Orchestration service allows the
use of templates to define a set of instances to be launched
together or for scaling existing sets. It can also be used to
set up matching or differentiated groupings based on
regions. For instance, if an application requires an equally
balanced number of nodes across sites, the same heat template
can be used to cover each site with small alterations to only
the region name.</para>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="user-requirements-multi-site">
<?dbhtml stop-chunking?>
<title>User requirements</title>
<section xml:id="workload-characteristics">
<title>Workload characteristics</title>
<para>An understanding of the expected workloads for a desired
multi-site environment and use case is an important factor in
the decision-making process. In this context, <literal>workload</literal>
refers to the way the systems are used. A workload could be a
single application or a suite of applications that work together.
It could also be a duplicate set of applications that need to
run in multiple cloud environments. Often in a multi-site deployment,
the same workload will need to work identically in more than one
physical location.</para>
<para>This multi-site scenario likely includes one or more of the
other scenarios in this book with the additional requirement
of having the workloads in two or more locations. The
following are some possible scenarios:</para>
<para>For many use cases the proximity of the user to their
workloads has a direct influence on the performance of the
application and therefore should be taken into consideration
in the design. Certain applications require zero to minimal
latency that can only be achieved by deploying the cloud in
multiple locations. These locations could be in different data
centers, cities, countries or geographical regions, depending
on the user requirement and location of the users.</para></section>
<section xml:id="consistency-images-templates-across-sites">
<title>Consistency of images and templates across different
sites</title>
<para>It is essential that the deployment of instances is
consistent across the different sites and built
into the infrastructure. If the OpenStack Object Storage is used as
a back end for the Image service, it is possible to create repositories
of consistent images across multiple sites. Having central
endpoints with multiple storage nodes allows consistent centralized
storage for every site.</para>
<para>Not using a centralized object store increases the operational
overhead of maintaining a consistent image library. This
could include development of a replication mechanism to handle
the transport of images and the changes to the images across
multiple sites.</para></section>
<section xml:id="high-availability-multi-site">
<title>High availability</title>
<para>If high availability is a requirement to provide continuous
infrastructure operations, a basic requirement of high
availability should be defined.</para>
<para>The OpenStack management components need to have a basic and
minimal level of redundancy. The simplest example is the loss
of any single site should have minimal impact on the
availability of the OpenStack services.</para>
<para>The <link
xlink:href="http://docs.openstack.org/ha-guide/"><citetitle>OpenStack
High Availability Guide</citetitle></link>
contains more information on how to provide redundancy for the
OpenStack components.</para>
<para>Multiple network links should be deployed between sites to
provide redundancy for all components. This includes storage
replication, which should be isolated to a dedicated network
or VLAN with the ability to assign QoS to control the
replication traffic or provide priority for this traffic. Note
that if the data store is highly changeable, the network
requirements could have a significant effect on the
operational cost of maintaining the sites.</para>
<para>The ability to maintain object availability in both sites
has significant implications on the object storage design and
implementation. It also has a significant impact on the
WAN network design between the sites.</para>
<para>Connecting more than two sites increases the challenges and
adds more complexity to the design considerations. Multi-site
implementations require planning to address the additional
topology used for internal and external connectivity. Some options
include full mesh topology, hub spoke, spine leaf, and 3D Torus.</para>
<para>If applications running in a cloud are not cloud-aware, there
should be clear measures and expectations to define what the
infrastructure can and cannot support. An example would be
shared storage between sites. It is possible, however such a
solution is not native to OpenStack and requires a third-party
hardware vendor to fulfill such a requirement. Another example
can be seen in applications that are able to consume resources
in object storage directly. These applications need to be
cloud aware to make good use of an OpenStack Object
Store.</para></section>
<section xml:id="application-readiness">
<title>Application readiness</title>
<para>Some applications are tolerant of the lack of synchronized
object storage, while others may need those objects to be
replicated and available across regions. Understanding how
the cloud implementation impacts new and existing applications
is important for risk mitigation, and the overall success of a
cloud project. Applications may have to be written or rewritten
for an infrastructure with little to no redundancy, or with the
cloud in mind.</para></section>
<section xml:id="cost-multi-site">
<title>Cost</title>
<para>A greater number of sites increase cost and complexity for a
multi-site deployment. Costs can be broken down into the following
categories:</para>
<itemizedlist>
<listitem>
<para>Compute resources</para>
</listitem>
<listitem>
<para>Networking resources</para>
</listitem>
<listitem>
<para>Replication</para>
</listitem>
<listitem>
<para>Storage</para>
</listitem>
<listitem>
<para>Management</para>
</listitem>
<listitem>
<para>Operational costs</para>
</listitem>
</itemizedlist></section>
<section xml:id="site-loss-and-recovery">
<title>Site loss and recovery</title>
<para>Outages can cause partial or full loss of site functionality.
Strategies should be implemented to understand and plan for recovery
scenarios.</para>
<itemizedlist>
<listitem>
<para>The deployed applications need to continue to
function and, more importantly, you must consider the
impact on the performance and reliability of the application
when a site is unavailable.</para>
</listitem>
<listitem>
<para>It is important to understand what happens to the
replication of objects and data between the sites when
a site goes down. If this causes queues to start
building up, consider how long these queues can
safely exist until an error occurs.</para>
</listitem>
<listitem>
<para>After an outage, ensure the method for resuming proper
operations of a site is implemented when it comes back online.
We recommend you architect the recovery to avoid race conditions.</para>
</listitem>
</itemizedlist></section>
<section xml:id="compliance-and-geo-location-multi-site">
<title>Compliance and geo-location</title>
<para>An organization may have certain legal obligations and
regulatory compliance measures which could require certain
workloads or data to not be located in certain regions.</para></section>
<section xml:id="auditing-multi-site">
<title>Auditing</title>
<para>A well thought-out auditing strategy is important in order
to be able to quickly track down issues. Keeping track of
changes made to security groups and tenant changes can be
useful in rolling back the changes if they affect production.
For example, if all security group rules for a tenant
disappeared, the ability to quickly track down the issue would
be important for operational and legal reasons.</para></section>
<section xml:id="separation-of-duties">
<title>Separation of duties</title>
<para>A common requirement is to define different roles for the
different cloud administration functions. An example would be
a requirement to segregate the duties and permissions by
site.</para></section>
<section xml:id="authentication-between-sites">
<title>Authentication between sites</title>
<para>It is recommended to have a single authentication domain
rather than a separate implementation for each and every
site. This requires an authentication mechanism that is highly
available and distributed to ensure continuous operation.
Authentication server locality might be required and should be
planned for.</para></section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="architecture-network-focus">
<title>Architecture</title>
<para>Network-focused OpenStack architectures have many similarities to
other OpenStack architecture use cases. There are several factors
to consider when designing for a network-centric or network-heavy
application environment.</para>
<para>Networks exist to serve as a medium of transporting data between
systems. It is inevitable that an OpenStack design has inter-dependencies
with non-network portions of OpenStack as well as on external systems.
Depending on the specific workload, there may be major interactions with
storage systems both within and external to the OpenStack environment.
For example, in the case of content delivery network, there is twofold
interaction with storage. Traffic flows to and from the storage array for
ingesting and serving content in a north-south direction. In addition,
there is replication traffic flowing in an east-west direction.</para>
<para>Compute-heavy workloads may also induce interactions with the
network. Some high performance compute applications require network-based
memory mapping and data sharing and, as a result, induce a higher network
load when they transfer results and data sets. Others may be highly
transactional and issue transaction locks, perform their functions, and
revoke transaction locks at high rates. This also has an impact on the
network performance.</para>
<para>Some network dependencies are external to OpenStack. While
OpenStack Networking is capable of providing network ports, IP addresses,
some level of routing, and overlay networks, there are some other
functions that it cannot provide. For many of these, you may require
external systems or equipment to fill in the functional gaps. Hardware
load balancers are an example of equipment that may be necessary to
distribute workloads or offload certain functions. OpenStack Networking
provides a tunneling feature, however it is constrained to a
Networking-managed region. If the need arises to extend a tunnel beyond
the OpenStack region to either another region or an external system,
implement the tunnel itself outside OpenStack or use a tunnel management
system to map the tunnel or overlay to an external tunnel.
</para>
<para>
Depending on the selected design, Networking itself might not
support the required <glossterm baseform="Layer-3 network">layer-3
network</glossterm> functionality. If you choose to use the
provider networking mode without running the layer-3 agent, you
must install an external router to provide layer-3 connectivity
to outside systems.
</para>
<para>Interaction with orchestration services is inevitable in
larger-scale deployments. The Orchestration service is capable of
allocating network resource defined in templates to map to tenant
networks and for port creation, as well as allocating floating IPs.
If there is a requirement to define and manage network resources when
using orchestration, we recommend that the design include the
Orchestration service to meet the demands of users.</para>
<section xml:id="design-impacts">
<title>Design impacts</title>
<para>A wide variety of factors can affect a network-focused OpenStack
architecture. While there are some considerations shared with a general
use case, specific workloads related to network requirements influence
network design decisions.</para>
<para>One decision includes whether or not to use Network Address
Translation (NAT) and where to implement it. If there is a requirement
for floating IPs instead of public fixed addresses then you must use
NAT. An example of this is a DHCP relay that must know the IP of the
DHCP server. In these cases it is easier to automate the infrastructure
to apply the target IP to a new instance rather than to reconfigure
legacy or external systems for each new instance.</para>
<para>NAT for floating IPs managed by Networking resides within the
hypervisor but there are also versions of NAT that may be running
elsewhere. If there is a shortage of IPv4 addresses there are two common
methods to mitigate this externally to OpenStack. The first is to run a
load balancer either within OpenStack as an instance, or use an external
load balancing solution. In the internal scenario, Networking's
Load-Balancer-as-a-Service (LBaaS) can manage load balancing
software, for example HAproxy. This is specifically to manage the
Virtual IP (VIP) while a dual-homed connection from the HAproxy instance
connects the public network with the tenant private network that hosts
all of the content servers. In the external scenario, a load balancer
needs to serve the VIP and also connect to the tenant overlay
network through external means or through private addresses.</para>
<para>Another kind of NAT that may be useful is protocol NAT. In some
cases it may be desirable to use only IPv6 addresses on instances and
operate either an instance or an external service to provide a NAT-based
transition technology such as NAT64 and DNS64. This provides the ability
to have a globally routable IPv6 address while only consuming IPv4
addresses as necessary or in a shared manner.</para>
<para>Application workloads affect the design of the underlying network
architecture. If a workload requires network-level redundancy, the
routing and switching architecture have to accommodate this. There
are differing methods for providing this that are dependent on the
selected network hardware, the performance of the hardware, and which
networking model you deploy. Examples include
Link aggregation (LAG) and Hot Standby Router Protocol (HSRP). Also
consider whether to deploy OpenStack Networking or
legacy networking (nova-network), and which plug-in to select for
OpenStack Networking. If using an external system, configure Networking
to run <glossterm baseform="Layer-2 network">layer 2</glossterm>
with a provider network configuration. For example, implement HSRP
to terminate layer-3 connectivity.</para>
<para>Depending on the workload, overlay networks may not be the best
solution. Where application network connections are
small, short lived, or bursty, running a dynamic overlay can generate
as much bandwidth as the packets it carries. It also can induce enough
latency to cause issues with certain applications. There is an impact
to the device generating the overlay which, in most installations,
is the hypervisor. This causes performance degradation on packet
per second and connection per second rates.</para>
<para>Overlays also come with a secondary option that may not be
appropriate to a specific workload. While all of them operate in full
mesh by default, there might be good reasons to disable this function
because it may cause excessive overhead for some workloads. Conversely,
other workloads operate without issue. For example, most web services
applications do not have major issues with a full mesh overlay network,
while some network monitoring tools or storage replication workloads
have performance issues with throughput or excessive broadcast
traffic.</para>
<para>Many people overlook an important design decision: The choice of
layer-3 protocols. While OpenStack was initially built with only IPv4
support, Networking now supports IPv6 and dual-stacked networks.
Some workloads are possible through the use of IPv6 and IPv6 to IPv4
reverse transition mechanisms such as NAT64 and DNS64 or
<glossterm>6to4</glossterm>.
This alters the requirements for any address plan as single-stacked and
transitional IPv6 deployments can alleviate the need for IPv4
addresses.</para>
<para>OpenStack has limited support for
dynamic routing, however there are a number of options available by
incorporating third party solutions to implement routing within the
cloud including network equipment, hardware nodes, and instances. Some
workloads perform well with nothing more than static routes and default
gateways configured at the layer-3 termination point. In most cases this
is sufficient, however some cases require the addition of at least one
type of dynamic routing protocol if not multiple protocols. Having a
form of interior gateway protocol (IGP) available to the instances
inside an OpenStack installation opens up the possibility of use cases
for anycast route injection for services that need to use it as a
geographic location or failover mechanism. Other applications may wish
to directly participate in a routing protocol, either as a passive
observer, as in the case of a looking glass, or as an active participant
in the form of a route reflector. Since an instance might have a large
amount of compute and memory resources, it is trivial to hold an entire
unpartitioned routing table and use it to provide services such as
network path visibility to other applications or as a monitoring
tool.</para>
<para>Path maximum transmission unit (MTU) failures are lesser known but
harder to diagnose. The MTU must be large enough to handle normal
traffic, overhead from an overlay network, and the desired layer-3
protocol. Adding externally built tunnels reduces the MTU packet size.
In this case, you must pay attention to the fully
calculated MTU size because some systems ignore or
drop path MTU discovery packets.</para>
</section>
<section xml:id="tunables">
<title>Tunable networking components</title>
<para>Consider configurable networking components related to an
OpenStack architecture design when designing for network intensive
workloads that include MTU and QoS. Some workloads require a larger MTU
than normal due to the transfer of large blocks of data.
When providing network service for applications such as video
streaming or storage replication, we recommend that you configure
both OpenStack hardware nodes and the supporting network equipment
for jumbo frames where possible. This allows for better use of
available bandwidth. Configure jumbo frames
across the complete path the packets traverse. If one network
component is not capable of handling jumbo frames then the entire
path reverts to the default MTU.</para>
<para>Quality of Service (QoS) also has a great impact on network
intensive workloads as it provides instant service to packets which
have a higher priority due to the impact of poor
network performance. In applications such as Voice over IP (VoIP),
differentiated services code points are a near requirement for proper
operation. You can also use QoS in the opposite direction for mixed
workloads to prevent low priority but high bandwidth applications,
for example backup services, video conferencing, or file sharing,
from blocking bandwidth that is needed for the proper operation of
other workloads. It is possible to tag file storage traffic as a
lower class, such as best effort or scavenger, to allow the higher
priority traffic through. In cases where regions within a cloud might
be geographically distributed it may also be necessary to plan
accordingly to implement WAN optimization to combat latency or
packet loss.</para>
</section>
</section>

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<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="operational-considerations-networking-focus">
<?dbhtml stop-chunking?>
<title>Operational considerations</title>
<para>Network-focused OpenStack clouds have a number of operational
considerations that influence the selected design, including:</para>
<itemizedlist>
<listitem>
<para>Dynamic routing of static routes</para>
</listitem>
<listitem>
<para>Service level agreements (SLAs)</para>
</listitem>
<listitem>
<para>Ownership of user management</para>
</listitem>
</itemizedlist>
<para>An initial network consideration is the selection of a telecom
company or transit provider.</para>
<para>Make additional design decisions about monitoring and alarming.
This can be an internal responsibility or the responsibility of the
external provider. In the case of using an external provider, service
level agreements (SLAs) likely apply. In addition, other operational
considerations such as bandwidth, latency, and jitter can be part of an
SLA.</para>
<para>Consider the ability to upgrade the infrastructure. As demand for
network resources increase, operators add additional IP address blocks
and add additional bandwidth capacity. In addition, consider managing
hardware and software life cycle events, for example upgrades,
decommissioning, and outages, while avoiding service interruptions for
tenants.</para>
<para>Factor maintainability into the overall network design. This
includes the ability to manage and maintain IP addresses as well as the
use of overlay identifiers including VLAN tag IDs, GRE tunnel IDs, and
MPLS tags. As an example, if you may need to change all of the IP
addresses on a network, a process known as renumbering, then the design
must support this function.</para>
<para>Address network-focused applications when considering certain
operational realities. For example, consider the impending exhaustion
of IPv4 addresses, the migration to IPv6, and the use of private
networks to segregate different types of traffic that an application
receives or generates. In the case of IPv4 to IPv6 migrations,
applications should follow best practices for storing IP addresses.
We recommend you avoid relying on IPv4 features that did not carry over
to the IPv6 protocol or have differences in implementation.</para>
<para>To segregate traffic, allow applications to create a private tenant
network for database and storage network traffic. Use a public network
for services that require direct client access from the internet. Upon
segregating the traffic, consider quality of service (QoS) and security
to ensure each network has the required level of service.</para>
<para>Finally, consider the routing of network traffic.
For some applications, develop a complex policy framework for
routing. To create a routing policy that satisfies business requirements,
consider the economic cost of transmitting traffic over expensive links
versus cheaper links, in addition to bandwidth, latency, and jitter
requirements.</para>
<para>Additionally, consider how to respond to network events. As an
example, how load transfers from one link to another during a
failure scenario could be a factor in the design. If you do not plan
network capacity correctly, failover traffic could overwhelm other ports
or network links and create a cascading failure scenario. In this case,
traffic that fails over to one link overwhelms that link and then moves
to the subsequent links until all network traffic stops.</para>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="prescriptive-example-large-scale-web-app">
<?dbhtml stop-chunking?>
<title>Prescriptive examples</title>
<para>An organization designs a large-scale web application with cloud
principles in mind. The application scales
horizontally in a bursting fashion and generates a high
instance count. The application requires an SSL connection to
secure data and must not lose connection state to individual
servers.</para>
<para>The figure below depicts an example design for this workload.
In this example, a hardware load balancer provides SSL offload
functionality and connects
to tenant networks in order to reduce address consumption.
This load balancer links to the routing architecture as it
services the VIP for the application. The router and load
balancer use the GRE tunnel ID of the
application's tenant network and an IP address within
the tenant subnet but outside of the address pool. This is to
ensure that the load balancer can communicate with the
application's HTTP servers without requiring the consumption
of a public IP address.</para>
<para>Because sessions persist until closed, the routing and
switching architecture provides high availability.
Switches mesh to each hypervisor and each other, and
also provide an MLAG implementation to ensure that layer-2
connectivity does not fail. Routers use VRRP
and fully mesh with switches to ensure layer-3 connectivity.
Since GRE is provides an overlay network, Networking is present
and uses the Open vSwitch agent in GRE tunnel
mode. This ensures all devices can reach all other devices and
that you can create tenant networks for private addressing
links to the load balancer.
<mediaobject>
<imageobject>
<imagedata contentwidth="4in"
fileref="../figures/Network_Web_Services1.png"
/>
</imageobject>
</mediaobject></para>
<para>A web service architecture has many options and optional
components. Due to this, it can fit into a large number of
other OpenStack designs. A few key components, however, need
to be in place to handle the nature of most web-scale
workloads. You require the following components:</para>
<itemizedlist>
<listitem>
<para>OpenStack Controller services (Image, Identity,
Networking and supporting services such as MariaDB and
RabbitMQ)</para>
</listitem>
<listitem>
<para>OpenStack Compute running KVM hypervisor</para>
</listitem>
<listitem>
<para>OpenStack Object Storage</para>
</listitem>
<listitem>
<para>Orchestration service</para>
</listitem>
<listitem>
<para>Telemetry service</para>
</listitem>
</itemizedlist>
<para>Beyond the normal Identity, Compute, Image service, and Object
Storage components, we recommend the Orchestration service
component to handle the proper scaling of workloads to adjust to
demand. Due to the requirement for auto-scaling,
the design includes the Telemetry service. Web services
tend to be bursty in load, have very defined peak and valley
usage patterns and, as a result, benefit from automatic scaling
of instances based upon traffic. At a network level, a split
network configuration works well with databases residing on
private tenant networks since these do not emit a large quantity
of broadcast traffic and may need to interconnect to some
databases for content.
</para>
<section xml:id="load-balancing">
<title>Load balancing</title>
<para>Load balancing spreads requests across multiple instances.
This workload scales well horizontally across large numbers of
instances. This enables instances to run without publicly
routed IP addresses and instead to rely on the load
balancer to provide a globally reachable service.
Many of these services do not require
direct server return. This aids in address planning and
utilization at scale since only the virtual IP (VIP) must be
public.</para>
</section>
<section xml:id="overlay-networks">
<title>Overlay networks</title>
<para>
The overlay functionality design includes OpenStack Networking
in Open vSwitch GRE tunnel mode.
In this case, the layer-3 external routers pair with
VRRP, and switches pair with an implementation of
MLAG to ensure that you do not lose connectivity with
the upstream routing infrastructure.
</para>
</section>
<section xml:id="performance-tuning">
<title>Performance tuning</title>
<para>Network level tuning for this workload is minimal.
Quality-of-Service (QoS) applies to these workloads
for a middle ground Class Selector depending on existing
policies. It is higher than a best effort queue but lower
than an Expedited Forwarding or Assured Forwarding queue.
Since this type of application generates larger packets with
longer-lived connections, you can optimize bandwidth utilization
for long duration TCP. Normal bandwidth planning
applies here with regards to benchmarking a session's usage
multiplied by the expected number of concurrent sessions with
overhead.</para>
</section>
<section xml:id="network-functions">
<title>Network functions</title>
<para>Network functions is a broad category but encompasses
workloads that support the rest of a system's network. These
workloads tend to consist of large amounts of small packets
that are very short lived, such as DNS queries or SNMP traps.
These messages need to arrive quickly and do not deal with
packet loss as there can be a very large volume of them. There
are a few extra considerations to take into account for this
type of workload and this can change a configuration all the
way to the hypervisor level. For an application that generates
10 TCP sessions per user with an average bandwidth of 512
kilobytes per second per flow and expected user count of ten
thousand concurrent users, the expected bandwidth plan is
approximately 4.88 gigabits per second.</para>
<para>The supporting network for this type of configuration needs
to have a low latency and evenly distributed availability.
This workload benefits from having services local to the
consumers of the service. Use a multi-site approach as
well as deploying many copies of the application to handle
load as close as possible to consumers. Since these
applications function independently, they do not warrant
running overlays to interconnect tenant networks. Overlays
also have the drawback of performing poorly with rapid flow
setup and may incur too much overhead with large quantities of
small packets and therefore we do not recommend them.</para>
<para>QoS is desirable for some workloads to ensure delivery. DNS
has a major impact on the load times of other services and
needs to be reliable and provide rapid responses. Configure rules
in upstream devices to apply a higher Class
Selector to DNS to ensure faster delivery or a better spot in
queuing algorithms.</para>
</section>
<section xml:id="cloud-storage">
<title>Cloud storage</title>
<para>Another common use case for OpenStack environments is providing
a cloud-based file storage and sharing service. You might
consider this a storage-focused use case, but its network-side
requirements make it a network-focused use case.</para>
<para>For example, consider a cloud backup application. This workload
has two specific behaviors that impact the network. Because this
workload is an externally-facing service and an
internally-replicating application, it has both <glossterm
baseform="north-south traffic">north-south</glossterm> and
<glossterm>east-west traffic</glossterm>
considerations:</para>
<variablelist>
<varlistentry>
<term>north-south traffic</term>
<listitem>
<para>When a user uploads and stores content, that content moves
into the OpenStack installation. When users download this
content, the content moves out from the OpenStack
installation. Because this service operates primarily
as a backup, most of the traffic moves southbound into the
environment. In this situation, it benefits you to
configure a network to be asymmetrically downstream
because the traffic that enters the OpenStack installation
is greater than the traffic that leaves the installation.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>east-west traffic</term>
<listitem>
<para>Likely to be fully symmetric. Because replication
originates from any node and might target multiple other
nodes algorithmically, it is less likely for this traffic
to have a larger volume in any specific direction. However
this traffic might interfere with north-south traffic.</para>
</listitem>
</varlistentry>
</variablelist>
<mediaobject>
<imageobject>
<imagedata contentwidth="4in"
fileref="../figures/Network_Cloud_Storage2.png"
/>
</imageobject>
</mediaobject>
<para>This application prioritizes the north-south traffic over
east-west traffic: the north-south traffic involves
customer-facing data.</para>
<para>The network design in this case is less dependent on
availability and more dependent on being able to handle high
bandwidth. As a direct result, it is beneficial to forgo
redundant links in favor of bonding those connections. This
increases available bandwidth. It is also beneficial to
configure all devices in the path, including OpenStack, to
generate and pass jumbo frames.</para>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
xmlns:xlink="http://www.w3.org/1999/xlink"
version="5.0"
xml:id="technical-considerations-network-focus">
<?dbhtml stop-chunking?>
<title>Technical considerations</title>
<para>When you design an OpenStack network architecture, you must
consider layer-2 and layer-3 issues. Layer-2
decisions involve those made at the data-link layer, such as
the decision to use Ethernet versus Token Ring. Layer-3 decisions
involve those made about the protocol layer and the point when
IP comes into the picture. As an example, a completely
internal OpenStack network can exist at layer 2 and ignore
layer 3. In order for any traffic to go outside of
that cloud, to another network, or to the Internet, however, you must
use a layer-3 router or switch.</para>
<para>The past few years have seen two competing trends in
networking. One trend leans towards building data center network
architectures based on layer-2 networking. Another trend treats
the cloud environment essentially as a miniature version of the
Internet. This approach is radically different from the network
architecture approach in the staging environment:
the Internet only uses layer-3 routing rather than
layer-2 switching.</para>
<para>A network designed on layer-2 protocols has advantages over one
designed on layer-3 protocols. In spite of the difficulties of
using a bridge to perform the network role of a router, many
vendors, customers, and service providers choose to use Ethernet
in as many parts of their networks as possible. The benefits of
selecting a layer-2 design are:</para>
<itemizedlist>
<listitem>
<para>Ethernet frames contain all the essentials for
networking. These include, but are not limited to,
globally unique source addresses, globally unique
destination addresses, and error control.</para>
</listitem>
<listitem>
<para>Ethernet frames can carry any kind of packet.
Networking at layer 2 is independent of the layer-3
protocol.</para>
</listitem>
<listitem>
<para>Adding more layers to the Ethernet frame only slows
the networking process down. This is known as 'nodal
processing delay'.</para>
</listitem>
<listitem>
<para>You can add adjunct networking features, for
example class of service (CoS) or multicasting, to
Ethernet as readily as IP networks.</para>
</listitem>
<listitem>
<para>VLANs are an easy mechanism for isolating
networks.</para>
</listitem>
</itemizedlist>
<para>Most information starts and ends inside Ethernet frames.
Today this applies to data, voice (for example, VoIP), and
video (for example, web cameras). The concept is that, if you can
perform more of the end-to-end transfer of information from
a source to a destination in the form of Ethernet frames, the network
benefits more from the advantages of Ethernet.
Although it is not a substitute for IP networking, networking at
layer 2 can be a powerful adjunct to IP networking.</para>
<para>
Layer-2 Ethernet usage has these advantages over layer-3 IP
network usage:
</para>
<itemizedlist>
<listitem>
<para>Speed</para>
</listitem>
<listitem>
<para>Reduced overhead of the IP hierarchy.</para>
</listitem>
<listitem>
<para>No need to keep track of address configuration as systems
move around. Whereas the simplicity of layer-2
protocols might work well in a data center with hundreds
of physical machines, cloud data centers have the
additional burden of needing to keep track of all virtual
machine addresses and networks. In these data centers, it
is not uncommon for one physical node to support 30-40
instances.</para>
</listitem>
</itemizedlist>
<important>
<para>Networking at the frame level says nothing
about the presence or absence of IP addresses at the packet
level. Almost all ports, links, and devices on a network of
LAN switches still have IP addresses, as do all the source and
destination hosts. There are many reasons for the continued
need for IP addressing. The largest one is the need to manage
the network. A device or link without an IP address is usually
invisible to most management applications. Utilities including
remote access for diagnostics, file transfer of configurations
and software, and similar applications cannot run without IP
addresses as well as MAC addresses.</para>
</important>
<section xml:id="layer-2-arch-limitations">
<title>Layer-2 architecture limitations</title>
<para>Outside of the traditional data center the limitations of
layer-2 network architectures become more obvious.</para>
<itemizedlist>
<listitem>
<para>Number of VLANs is limited to 4096.</para>
</listitem>
<listitem>
<para>The number of MACs stored in switch tables is
limited.</para>
</listitem>
<listitem>
<para>You must accommodate the need to maintain a set of
layer-4 devices to handle traffic control.</para>
</listitem>
<listitem>
<para>MLAG, often used for switch redundancy, is a
proprietary solution that does not scale beyond two
devices and forces vendor lock-in.</para>
</listitem>
<listitem>
<para>It can be difficult to troubleshoot a network
without IP addresses and ICMP.</para>
</listitem>
<listitem>
<para>Configuring <glossterm
baseform="Address Resolution Protocol (ARP)">ARP</glossterm>
can be complicated on large layer-2 networks.</para>
</listitem>
<listitem>
<para>All network devices need to be aware of all MACs,
even instance MACs, so there is constant churn in MAC
tables and network state changes as instances start and
stop.</para>
</listitem>
<listitem>
<para>Migrating MACs (instance migration) to different
physical locations are a potential problem if you do not
set ARP table timeouts properly.</para>
</listitem>
</itemizedlist>
<para>It is important to know that layer 2 has a very limited set
of network management tools. It is very difficult to control
traffic, as it does not have mechanisms to manage the network
or shape the traffic, and network troubleshooting is very
difficult. One reason for this difficulty is network devices
have no IP addresses. As a result, there is no reasonable way
to check network delay in a layer-2 network.</para>
<para>On large layer-2 networks, configuring ARP learning can also
be complicated. The setting for the MAC address timer on
switches is critical and, if set incorrectly, can cause
significant performance problems. As an example, the Cisco
default MAC address timer is extremely long. Migrating MACs to
different physical locations to support instance migration can
be a significant problem. In this case, the network
information maintained in the switches could be out of sync
with the new location of the instance.</para>
<para>In a layer-2 network, all devices are aware of all MACs,
even those that belong to instances. The network state
information in the backbone changes whenever an instance starts
or stops. As a result there is far too much churn in
the MAC tables on the backbone switches.</para>
</section>
<section xml:id="layer-3-arch-advantages">
<title>Layer-3 architecture advantages</title>
<para>In the layer 3 case, there is no churn in the routing tables
due to instances starting and stopping. The only time there
would be a routing state change is in the case of a Top
of Rack (ToR) switch failure or a link failure in the backbone
itself. Other advantages of using a layer-3 architecture
include:</para>
<itemizedlist>
<listitem>
<para>Layer-3 networks provide the same level of
resiliency and scalability as the Internet.</para>
</listitem>
<listitem>
<para>Controlling traffic with routing metrics is
straightforward.</para>
</listitem>
<listitem>
<para>You can configure layer 3 to use <glossterm
baseform="Border Gateway Protocol (BGP)">BGP</glossterm>
confederation for scalability so core routers have state
proportional to the number of racks, not to the number of
servers or instances.</para>
</listitem>
<listitem>
<para>Routing takes instance MAC and IP addresses
out of the network core, reducing state churn. Routing
state changes only occur in the case of a ToR switch
failure or backbone link failure.</para>
</listitem>
<listitem>
<para>There are a variety of well tested tools, for
example ICMP, to monitor and manage traffic.</para>
</listitem>
<listitem>
<para>Layer-3 architectures enable the use of Quality
of Service (QoS) to manage network performance.</para>
</listitem>
</itemizedlist>
<section xml:id="layer-3-arch-limitations">
<title>Layer-3 architecture limitations</title>
<para>The main limitation of layer 3 is that there is no built-in
isolation mechanism comparable to the VLANs in layer-2
networks. Furthermore, the hierarchical nature of IP addresses
means that an instance is on the same subnet as its
physical host. This means that you cannot migrate it outside
of the subnet easily. For these reasons, network
virtualization needs to use IP <glossterm>encapsulation</glossterm>
and software at the end hosts for isolation and the separation of
the addressing in the virtual layer from the addressing in the
physical layer. Other potential disadvantages of layer 3
include the need to design an IP addressing scheme rather than
relying on the switches to keep track of the MAC
addresses automatically and to configure the interior gateway routing
protocol in the switches.</para>
</section>
</section>
<section xml:id="network-recommendations-overview">
<title>Network recommendations overview</title>
<para>OpenStack has complex networking requirements for several
reasons. Many components interact at different levels of the
system stack that adds complexity. Data flows are complex.
Data in an OpenStack cloud moves both between instances across
the network (also known as East-West), as well as in and out
of the system (also known as North-South). Physical server
nodes have network requirements that are independent of instance
network requirements, which you must isolate from the core
network to account for scalability. We recommend
functionally separating the networks for security purposes and
tuning performance through traffic shaping.</para>
<para>You must consider a number of important general technical
and business factors when planning and
designing an OpenStack network. They include:</para>
<itemizedlist>
<listitem>
<para>A requirement for vendor independence. To avoid
hardware or software vendor lock-in, the design should
not rely on specific features of a vendor's router or
switch.</para>
</listitem>
<listitem>
<para>A requirement to massively scale the ecosystem to
support millions of end users.</para>
</listitem>
<listitem>
<para>A requirement to support indeterminate platforms and
applications.</para>
</listitem>
<listitem>
<para>A requirement to design for cost efficient
operations to take advantage of massive scale.</para>
</listitem>
<listitem>
<para>A requirement to ensure that there is no single
point of failure in the cloud ecosystem.</para>
</listitem>
<listitem>
<para>A requirement for high availability architecture to
meet customer SLA requirements.</para>
</listitem>
<listitem>
<para>A requirement to be tolerant of rack level
failure.</para>
</listitem>
<listitem>
<para>A requirement to maximize flexibility to architect
future production environments.</para>
</listitem>
</itemizedlist>
<para>Bearing in mind these considerations, we recommend the following:</para>
<itemizedlist>
<listitem>
<para>Layer-3 designs are preferable to layer-2
architectures.</para>
</listitem>
<listitem>
<para>Design a dense multi-path network core to support
multi-directional scaling and flexibility.</para>
</listitem>
<listitem>
<para>Use hierarchical addressing because it is the only
viable option to scale network ecosystem.</para>
</listitem>
<listitem>
<para>Use virtual networking to isolate instance service
network traffic from the management and internal
network traffic.</para>
</listitem>
<listitem>
<para>Isolate virtual networks using encapsulation
technologies.</para>
</listitem>
<listitem>
<para>Use traffic shaping for performance tuning.</para>
</listitem>
<listitem>
<para>Use eBGP to connect to the Internet up-link.</para>
</listitem>
<listitem>
<para>Use iBGP to flatten the internal traffic on the
layer-3 mesh.</para>
</listitem>
<listitem>
<para>Determine the most effective configuration for block
storage network.</para>
</listitem>
</itemizedlist></section>
<section xml:id="additional-considerations-network-focus">
<title>Additional considerations</title>
<para>There are several further considerations when designing a
network-focused OpenStack cloud.</para>
<section xml:id="openstack-networking-versus-nova-network">
<title>OpenStack Networking versus legacy networking (nova-network)
considerations</title>
<para>Selecting the type of networking technology to implement
depends on many factors. OpenStack Networking (neutron) and
legacy networking (nova-network) both have their advantages and
disadvantages. They are both valid and supported options that fit
different use cases:</para>
<informaltable rules="all">
<col width="40%" />
<col width="60%" />
<thead>
<tr><th>Legacy networking (nova-network)</th>
<th>OpenStack Networking</th></tr>
</thead>
<tbody>
<tr>
<td>Simple, single agent</td>
<td>Complex, multiple agents</td>
</tr>
<tr>
<td>More mature, established</td>
<td>Newer, maturing</td>
</tr>
<tr>
<td>Flat or VLAN</td>
<td>Flat, VLAN, Overlays, L2-L3, SDN</td></tr>
<tr>
<td>No plug-in support</td>
<td>Plug-in support for 3rd parties</td>
</tr>
<tr>
<td>Scales well</td>
<td>Scaling requires 3rd party plug-ins</td>
</tr>
<tr>
<td>No multi-tier topologies</td>
<td>Multi-tier topologies</td>
</tr>
</tbody>
</informaltable>
</section>
<section xml:id="redundant-networking-tor-switch-ha">
<title>Redundant networking: ToR switch high availability
risk analysis</title>
<para>A technical consideration of networking is the idea that
you should install switching gear in a data center
with backup switches in case of hardware failure.</para>
<para>Research indicates the mean time between failures (MTBF) on switches
is between 100,000 and 200,000 hours. This number is dependent
on the ambient temperature of the switch in the data
center. When properly cooled and maintained, this translates to
between 11 and 22 years before failure. Even in the worst case
of poor ventilation and high ambient temperatures in the data
center, the MTBF is still 2-3 years. See <link
xlink:href="http://www.garrettcom.com/techsupport/papers/ethernet_switch_reliability.pdf">http://www.garrettcom.com/techsupport/papers/ethernet_switch_reliability.pdf</link>
for further information.</para>
<para>In most cases, it is much more economical to use a
single switch with a small pool of spare switches to replace
failed units than it is to outfit an entire data center with
redundant switches. Applications should tolerate rack level
outages without affecting normal
operations, since network and compute resources are easily
provisioned and plentiful.</para>
</section>
<section xml:id="preparing-for-future-ipv6-support">
<title>Preparing for the future: IPv6 support</title>
<para>One of the most important networking topics today is the
impending exhaustion of IPv4 addresses. In early 2014, ICANN
announced that they started allocating the final IPv4 address
blocks to the Regional Internet Registries (<link
xlink:href="http://www.internetsociety.org/deploy360/blog/2014/05/goodbye-ipv4-iana-starts-allocating-final-address-blocks/">http://www.internetsociety.org/deploy360/blog/2014/05/goodbye-ipv4-iana-starts-allocating-final-address-blocks/</link>).
This means the IPv4 address space is close to being fully
allocated. As a result, it will soon become difficult to
allocate more IPv4 addresses to an application that has
experienced growth, or that you expect to scale out, due to the lack
of unallocated IPv4 address blocks.</para>
<para>For network focused applications the future is the IPv6
protocol. IPv6 increases the address space significantly,
fixes long standing issues in the IPv4 protocol, and will
become essential for network focused applications in the
future.</para>
<para>OpenStack Networking supports IPv6 when configured to take
advantage of it. To enable IPv6, create an IPv6 subnet in
Networking and use IPv6 prefixes when creating security
groups.</para></section>
<section xml:id="asymmetric-links">
<title>Asymmetric links</title>
<para>When designing a network architecture, the traffic patterns
of an application heavily influence the allocation of
total bandwidth and the number of links that you use to send
and receive traffic. Applications that provide file storage
for customers allocate bandwidth and links to favor
incoming traffic, whereas video streaming applications
allocate bandwidth and links to favor outgoing traffic.</para>
</section>
<section xml:id="performance-network-focus">
<title>Performance</title>
<para>It is important to analyze the applications' tolerance for
latency and jitter when designing an environment to support
network focused applications. Certain applications, for
example VoIP, are less tolerant of latency and jitter. Where
latency and jitter are concerned, certain applications may
require tuning of QoS parameters and network device queues to
ensure that they queue for transmit immediately or
guarantee minimum bandwidth. Since OpenStack currently does
not support these functions, consider carefully your selected
network plug-in.</para>
<para>The location of a service may also impact the application or
consumer experience. If an application serves
differing content to different users it must properly direct
connections to those specific locations. Where appropriate,
use a multi-site installation for these situations.</para>
<para>You can implement networking in two separate
ways. Legacy networking (nova-network) provides a flat DHCP network
with a single broadcast domain. This implementation does not
support tenant isolation networks or advanced plug-ins, but it
is currently the only way to implement a distributed layer-3
agent using the multi_host configuration.
OpenStack Networking (neutron) is the official networking implementation
and provides a pluggable architecture that supports a large
variety of network methods. Some of these include a layer-2
only provider network model, external device plug-ins, or even
OpenFlow controllers.</para>
<para>Networking at large scales becomes a set of boundary
questions. The determination of how large a layer-2 domain
must be is based on the amount of nodes within the domain
and the amount of broadcast traffic that passes between
instances. Breaking layer-2 boundaries may require the
implementation of overlay networks and tunnels. This decision
is a balancing act between the need for a smaller overhead or
a need for a smaller domain.</para>
<para>When selecting network devices, be aware that making this
decision based on the greatest port density often comes with a
drawback. Aggregation switches and routers have not all kept
pace with Top of Rack switches and may induce bottlenecks on
north-south traffic. As a result, it may be possible for
massive amounts of downstream network utilization to impact
upstream network devices, impacting service to the cloud.
Since OpenStack does not currently provide a mechanism for
traffic shaping or rate limiting, it is necessary to implement
these features at the network hardware level.</para>
</section>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<section xmlns="http://docbook.org/ns/docbook"
xmlns:xi="http://www.w3.org/2001/XInclude"
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xml:id="user-requirements-network-focus">
<?dbhtml stop-chunking?>
<title>User requirements</title>
<para>Network-focused architectures vary from the general-purpose
architecture designs. Certain network-intensive applications influence
these architectures. Some of the business requirements that influence
the design include:</para>
<itemizedlist>
<listitem>
<para>Network latency through slow page loads, degraded video
streams, and low quality VoIP sessions impacts the user
experience. Users are often not aware of how network design and
architecture affects their experiences. Both enterprise customers
and end-users rely on the network for delivery of an application.
Network performance problems can result in a negative experience
for the end-user, as well as productivity and economic loss.
</para>
</listitem>
</itemizedlist>
<section xml:id="high-availability-issues-network-focus">
<title>High availability issues</title>
<para>Depending on the application and use case, network-intensive
OpenStack installations can have high availability requirements.
Financial transaction systems have a much higher requirement for high
availability than a development application. Use network availability
technologies, for example quality of service (QoS), to improve the
network performance of sensitive applications such as VoIP and video
streaming.</para>
<para>High performance systems have SLA requirements for a minimum
QoS with regard to guaranteed uptime, latency, and bandwidth. The level
of the SLA can have a significant impact on the network architecture and
requirements for redundancy in the systems.</para>
</section>
<section xml:id="risks-network-focus">
<title>Risks</title>
<variablelist>
<varlistentry>
<term>Network misconfigurations</term>
<listitem>
<para>Configuring incorrect IP addresses, VLANs, and routers
can cause outages to areas of the network or, in the worst-case
scenario, the entire cloud infrastructure. Automate network
configurations to minimize the opportunity for operator error
as it can cause disruptive problems.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Capacity planning</term>
<listitem>
<para>Cloud networks require management for capacity and growth
over time. Capacity planning includes the purchase of network
circuits and hardware that can potentially have lead times
measured in months or years.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Network tuning</term>
<listitem>
<para>Configure cloud networks to minimize link loss, packet loss,
packet storms, broadcast storms, and loops.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Single Point Of Failure (SPOF)</term>
<listitem>
<para>Consider high availability at the physical and environmental
layers. If there is a single point of failure due to only one
upstream link, or only one power supply, an outage can become
unavoidable.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Complexity</term>
<listitem>
<para>An overly complex network design can be difficult to
maintain and troubleshoot. While device-level configuration
can ease maintenance concerns and automated tools can handle
overlay networks, avoid or document non-traditional interconnects
between functions and specialized hardware to prevent
outages.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Non-standard features</term>
<listitem>
<para>There are additional risks that arise from configuring the
cloud network to take advantage of vendor specific features.
One example is multi-link aggregation (MLAG) used to provide
redundancy at the aggregator switch level of the network. MLAG
is not a standard and, as a result, each vendor has their own
proprietary implementation of the feature. MLAG architectures
are not interoperable across switch vendors, which leads to
vendor lock-in, and can cause delays or inability when upgrading
components.</para>
</listitem>
</varlistentry>
</variablelist>
</section>
</section>

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<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<parent>
<groupId>org.openstack.docs</groupId>
<artifactId>parent-pom</artifactId>
<version>1.0.0-SNAPSHOT</version>
<relativePath>../pom.xml</relativePath>
</parent>
<modelVersion>4.0.0</modelVersion>
<artifactId>openstack-arch-design</artifactId>
<packaging>jar</packaging>
<name>OpenStack Architecture Design Guide</name>
<properties>
<!-- This is set by Jenkins according to the branch. -->
<release.path.name></release.path.name>
<comments.enabled>0</comments.enabled>
</properties>
<!-- ################################################ -->
<!-- USE "mvn clean generate-sources" to run this POM -->
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<build>
<plugins>
<plugin>
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<artifactId>clouddocs-maven-plugin</artifactId>
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<executions>
<execution>
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<goals>
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</goals>
<phase>generate-sources</phase>
<configuration>
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<enableGoogleAnalytics>1</enableGoogleAnalytics>
<googleAnalyticsId>UA-17511903-1</googleAnalyticsId>
<generateToc>
appendix toc,title
article/appendix nop
article toc,title
book toc,title,figure,table,example,equation
chapter toc,title
section toc
part toc,title
qandadiv toc
qandaset toc
reference toc,title
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<configuration>
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<sourceDirectory>.</sourceDirectory>
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