openstack-manuals/doc/arch-design/generalpurpose/section_tech_considerations_general_purpose.xml

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  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>For example, if you wanted to design a hardware node as a compute resource
      pool to service instances, consider the number of processor cores available
      on the node as well as the required disk and memory to service instances
      running at capacity. For a server with 2 CPUs of 10 cores each, with
      hyperthreading turned on, the default CPU overcommit ratio of 16:1 would allow
      for 640 (2 &times; 10 &times; 2 &times; 16) total <literal>m1.small</literal>
      instances, where each instance uses 1 vCPU, 20&nbsp;GB of ephemeral storage
      and 2,048&nbsp;MB of RAM.  By the same reasoning, using the default memory
      overcommit ratio of 1.5:1 you can determine that the server will need at least
      853&nbsp;GB (640 &times; 2,048&nbsp;MB / 1.5) of RAM. When sizing nodes for
      memory, it is also important to consider the additional memory required to
      service operating system and service needs.</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>Initially, we recommend you design at least three network segments.</para>
    <para>The first segment is a public network, used for access to REST APIs
        by tenants and operators. Generally, the controller nodes and swift
        proxies will be 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>
    <para>The second segment is used by administrators to manage hardware resources.
        It is also used by configuration management tools 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 will probably need to communicate with every hardware node.
        Due to the highly secure nature of this network segment, you will also need to
        secure this network from unauthorized access.</para>
    <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
        generally 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 will need to communicate on this network segment, as
        will any network gateway services which allow application data to access the
        physical network from outside of the cloud.</para>
    </section>

    <section xml:id="designing-storage-resources-tech-considerations">
      <title>Designing storage resources</title>
      <para>OpenStack has two independent storage services to consider,
        each with its own specific design requirements and goals. In
        addition to services which provide storage as their primary
        function, there are additional design considerations with
        regard to compute and controller nodes which will affect the
        overall cloud architecture.</para> <!--Could there be room for more tech content here? A.S-->
    </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>
    <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 will ensure that data stays up to date and survives
        hardware faults without the use of any specialized data
        replication devices.</para>
    <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. Many server chassis on the
        market can hold 60 or more drives in 4U of rack space,
        therefore we recommend maximizing the amount of storage
        per rack unit at the best cost per terabyte. Furthermore, we
        do not recommend the use of RAID controllers in an object storage
        node.</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 defult 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. As an example, for
        a general purpose cloud that predominantly supports a
        Microsoft-based migration, or is managed by staff that has a
        particular skill for managing certain hypervisors and
        operating systems, Hyper-V would be the best available choice.
        While the decision to use Hyper-V does not limit the ability
        to run alternative operating systems, be mindful of those that
        are deemed supported. Each different hypervisor also has their
        own hardware requirements which may affect the decisions
        around designing a general purpose cloud. For example, to
        utilize the live migration feature of VMware, vMotion, this
        requires an installation of vCenter/vSphere and the use of the
        ESXi hypervisor, which increases the infrastructure
        requirements.</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> module
            (<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>
      <note>
        <para>However, depending on the use case, these could be
        optional.</para>
      </note>
    </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. Therefore,
        the underlying database nodes, for example, should consist of
        at least 3 nodes to account for the recovery of a failed
        Galera node. When increasing the number of nodes to support a
        feature of the software, consideration of rack space and
        switch port density becomes important.</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="performance-tech-considerations">
      <title>Performance</title>
    <para>Performance of an OpenStack deployment is dependent on a
        number of factors related to the infrastructure and controller
        services. The user requirements can be split into general
        network performance, performance of compute resources, and
        performance of storage systems.</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. For
        example, small deployments may employ 1 Gigabit Ethernet (GbE)
        networking, whereas larger installations serving multiple
        departments or many users would be better architected with
        10&nbsp;GbE networking. The performance of the running instances will
        be limited by these speeds. 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>For example, web application instances may run
        on a public network presented through OpenStack Networking
        that has 1 GbE capability, whereas the back-end database uses
        an OpenStack Networking network that has 10&nbsp;GbE capability to
        replicate its data or, in some cases, the design may
        incorporate link aggregation for greater throughput.</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. As
        an example, in a deployment that has two infrastructure
        controller nodes, the design should include controller
        availability. In the event of the loss of a single controller,
        cloud services will run from a single controller in the event
        of failure. Where the design has higher availability
        requirements, it is important to meet those requirements by
        designing the proper redundancy and availability of controller
        nodes.</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. Conversely, 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/high-availability-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. For example, some
        deployment topologies combine both guest and data domains onto
        one physical network, whereas in other cases these networks
        are physically separated. 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>
    <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>
    <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>
    <para>The management security domain is where services interact.
        Sometimes referred to as the "control plane", 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>
    <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>
    <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,
        traditionally, 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. For example, the API endpoints, along with the
        software behind them, become vulnerable to bad actors wanting
        to gain unauthorized access or prevent access to services,
        which could lead to loss of data, functionality, and
        reputation. These services must be protected against through
        auditing and appropriate filtering.</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's 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>