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