90 lines
4.7 KiB
XML
90 lines
4.7 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="multi-hypervisor-example">
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<?dbhtml stop-chunking?>
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<title>Multi-hypervisor example</title>
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<para>A financial company requires the migration of its applications
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from a traditional virtualized environment to an API driven,
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orchestrated environment. Many of their applications have
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strict hypervisor support requirements, but others do not have
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the same restrictions and do not need the same features. Because of
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these requirements, the overall target environment needs
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multiple hypervisors.</para>
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<para>The current environment consists of a vSphere environment
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with 20 VMware ESXi hypervisors supporting 300 instances of
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various sizes. Approximately 50 of the instances must run
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on ESXi but the rest have more flexible requirements.</para>
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<para>The company decides to bring the management of the
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overall system into a common OpenStack platform.</para>
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<mediaobject>
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<imageobject>
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<imagedata contentwidth="4in" fileref="../figures/Compute_NSX.png"/>
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</imageobject>
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</mediaobject>
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<para>The approach is to run a host aggregate consisting of KVM
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hypervisors for the general purpose instances and a separate
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host aggregate for instances requiring ESXi. This way,
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workloads that must run on ESXi can target those
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hypervisors, but the rest target the KVM
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hypervisors.</para>
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<para>Images in the OpenStack Image service have particular
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hypervisor metadata attached so that when a user requests a
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certain image, the instance spawns on the relevant
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aggregate. Images for ESXi use the VMDK format. You can convert
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QEMU disk images to VMDK, VMFS Flat Disks, which
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includes thin, thick, zeroed-thick, and eager-zeroed-thick.
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Note that after you export a VMFS thin disk from VMFS to a
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non-VMFS location, for example the OpenStack Image service, it
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becomes a preallocated flat disk. This impacts the transfer
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time from the OpenStack Image service to the data store as it
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requires moving the full preallocated flat disk rather than the
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thin disk.</para>
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<para>This example has the additional complication that, rather
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than spawning directly on a hypervisor by calling
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a specific host aggregate using the metadata of the image, the
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VMware host aggregate compute nodes communicate with vCenter
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which then requests scheduling for the instance to run on
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an ESXi hypervisor. As of the Icehouse release, this
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functionality requires that VMware Distributed Resource
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Scheduler (DRS) is enabled on a cluster and set to "Fully
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Automated".</para>
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<para>Due to the DRS requirement, note that vSphere requires
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shared storage (DRS uses vMotion, which requires shared
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storage). This solution uses shared storage to provide Block
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Storage capabilities to the KVM instances while also providing
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the storage for vSphere. The environment uses a dedicated data
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network to provide this functionality, therefore the compute
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hosts should have dedicated NICs to support this dedicated
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traffic. vSphere supports the use of OpenStack Block Storage
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to present storage from a VMFS datastore to an instance, so
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the use of Block Storage in this architecture supports both
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hypervisors.</para>
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<para>In this case, OpenStack Networking provides network connectivity
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with the VMware NSX plug-in driver configured. Alternatively,
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the system can use legacy networking (nova-network), which both
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hypervisors in this design support, but has
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limitations. Specifically, vSphere with legacy networking does
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not support security groups. With VMware NSX as part of the
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design, however, when a user launches an instance within
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either of the host aggregates, the instances attach to
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appropriate network overlay-based logical networks as defined
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by the user.</para>
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<para>There are design considerations around OpenStack Compute
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integration. When using vSphere with OpenStack, the
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nova-compute service communicating with
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vCenter shows up as a single large hypervisor representing the
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entire ESXi cluster (multiple instances of nova-compute can
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represent multiple ESXi clusters or connect to
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multiple vCenter servers). If the process running the
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nova-compute service crashes, it severs the connection to that
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particular vCenter Server, and any ESXi clusters behind it,
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and it cannot provision further
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instances on that vCenter, despite the fact that you can configure
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vSphere for high availability. Therefore, you must monitor the
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nova-compute service that
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connects to vSphere for any disruptions.</para>
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</section>
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