b0337e125c
Replaced 'metrics' with 'meters' in all contexts, excluding the metric system or where the term is used as name. Change-Id: If4c32dfe92c28a2079a485a6aec1d61c7b9999a1 Closes-Bug: #1446518
165 lines
8.1 KiB
XML
165 lines
8.1 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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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="operational-considerations-general-purpose">
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<?dbhtml stop-chunking?>
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<title>Operational considerations</title>
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<para>In the planning and design phases of the build out, it is
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important to include the operation's function. Operational
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factors affect the design choices for a general purpose cloud,
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and operations staff are often tasked with the maintenance of
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cloud environments for larger installations.</para>
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<para>Knowing when and where to implement redundancy and high
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availability is directly affected by expectations set by the terms
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of the Service Level Agreements (SLAs). SLAs are contractual
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obligations that provide assurances for service availability.
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They define the levels of availability that drive the technical
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design, often with penalties for not meeting contractual obligations.</para>
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<para>SLA terms that will affect the design include:</para>
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<itemizedlist>
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<listitem>
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<para>API availability guarantees implying multiple
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infrastructure services, and highly available
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load balancers.</para>
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</listitem>
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<listitem>
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<para>Network uptime guarantees affecting switch
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design, which might require redundant switching and
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power.</para>
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</listitem>
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<listitem>
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<para>Network security policies requirements need to be
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factored in to deployments.</para>
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</listitem>
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</itemizedlist>
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<section xml:id="support-and-maintainability-general-purpose">
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<title>Support and maintainability</title>
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<para>To be able to support and maintain an installation, OpenStack
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cloud management requires operations staff to understand and
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comprehend design architecture content. The operations and engineering
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staff skill level, and level of separation, are dependent on size and
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purpose of the installation. Large cloud service providers, or telecom
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providers, are more likely to be managed by a specially trained, dedicated
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operations organization. Smaller implementations are more likely to rely
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on support staff that need to take on combined engineering, design and
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operations functions.</para>
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<para>Maintaining OpenStack installations requires a
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variety of technical skills. For example, if you are to incorporate features
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into an architecture and design that reduce the operations burden,
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it is advised to automate the operations functions. It may, however,
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be beneficial to use third party management companies with special
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expertise in managing OpenStack deployment.</para>
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</section>
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<section xml:id="monitoring-general-purpose">
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<title>Monitoring</title>
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<para>OpenStack clouds require appropriate monitoring platforms to
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ensure errors are caught and managed appropriately. Specific
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meters that are critically important to monitor include:</para>
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<itemizedlist>
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<listitem>
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<para>
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Image disk utilization
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</para>
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</listitem>
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<listitem>
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<para>
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Response time to the Compute API
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</para>
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</listitem>
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</itemizedlist>
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<para>Leveraging existing monitoring systems is an effective check to
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ensure OpenStack environments can be monitored.</para>
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</section>
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<section xml:id="downtime-general-purpose">
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<title>Downtime</title>
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<para>To effectively run cloud installations, initial downtime planning
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includes creating processes and architectures that support
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the following:</para>
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<itemizedlist>
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<listitem>
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<para>
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Planned (maintenance)
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</para>
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</listitem>
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<listitem>
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<para>
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Unplanned (system faults)
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</para>
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</listitem>
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</itemizedlist>
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<para>Resiliency of overall system and individual components are going
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to be dictated by the requirements of the SLA, meaning designing
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for high availability (HA) can have cost ramifications.</para>
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<para>For example, if a compute host failed, this would be an operational
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consideration; requiring the restoration of instances from a
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snapshot or re-spawning an instance. The overall application design
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is impacted, general purpose clouds should not need to provide
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abilities to migrate instances from one host to another. Additional
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considerations need to be made around supporting instance migration if
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the expectation is that the application will be designed to tolerate
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failure. Extra support services, including shared storage attached to
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compute hosts, might need to be deployed in this example.</para>
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</section>
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<section xml:id="capacity-planning">
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<title>Capacity planning</title>
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<para>Capacity constraints for a general purpose cloud environment
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include:</para>
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<itemizedlist>
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<listitem>
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<para>
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Compute limits
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</para>
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</listitem>
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<listitem>
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<para>
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Storage limits
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</para>
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</listitem>
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</itemizedlist>
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<para>A relationship exists between the size of the compute environment
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and the supporting OpenStack infrastructure controller nodes requiring
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support.</para>
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<para>Increasing the size of the supporting compute environment increases
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the network traffic and messages, adding load to the controller or
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networking nodes. Effective monitoring of the environment will help
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with capacity decisions on scaling.</para>
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<para>Compute nodes automatically attach to OpenStack clouds, resulting in
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a horizontally scaling process when adding extra compute capacity to an
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OpenStack cloud. Additional processes are required to place nodes into
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appropriate availability zones and host aggregates. When adding additional
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compute nodes to environments, ensure identical or functional compatible
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CPUs are used, otherwise live migration features will break. It is necessary
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to add rack capacity or network switches as scaling out compute hosts directly
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affects network and datacenter resources.</para>
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<para>Assessing the average workloads and increasing the number of instances
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that can run within the compute environment by adjusting the overcommit
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ratio is another option. It is important to remember that changing the CPU overcommit
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ratio can have a detrimental effect and cause a potential increase in a
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noisy neighbor. The additional risk of increasing the overcommit ratio is
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more instances failing when a compute host fails.</para>
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<para>Compute host components can also be upgraded to account for
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increases in demand; this is known as vertical scaling.
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Upgrading CPUs with more cores, or increasing the overall
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server memory, can add extra needed capacity depending on
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whether the running applications are more CPU intensive or
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memory intensive.</para>
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<para>Insufficient disk capacity could also have a negative effect
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on overall performance including CPU and memory usage.
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Depending on the back-end architecture of the OpenStack Block
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Storage layer, capacity includes adding disk shelves to
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enterprise storage systems or installing additional block
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storage nodes. Upgrading directly attached storage installed in
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compute hosts, and adding capacity to the shared storage for
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additional ephemeral storage to instances, may be necessary.</para>
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<para>
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For a deeper discussion on many of these topics, refer to the
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<link
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xlink:href="http://docs.openstack.org/ops"><citetitle>OpenStack
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Operations Guide</citetitle></link>.
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</para>
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</section>
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</section>
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