81 lines
4.5 KiB
XML
81 lines
4.5 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 its applications migrated
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from a traditional, virtualized environment to an API driven,
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orchestrated environment. The new environment needs
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multiple hypervisors since many of the company's applications
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have strict hypervisor requirements.</para>
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<para>Currently, the company's vSphere environment runs 20 VMware
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ESXi hypervisors. These hypervisors support 300 instances of
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various sizes. Approximately 50 of these instances must run
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on ESXi. The remaining 250 or so have more flexible
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requirements.</para>
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<para>The financial company decides to manage the
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overall system with 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>Architecture planning teams decided to run a host aggregate
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containing KVM hypervisors for the general purpose instances. A
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separate host aggregate targets instances requiring ESXi.</para>
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<para>Images in the OpenStack Image service have particular
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hypervisor metadata attached. When a user requests a
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certain image, the instance spawns on the relevant
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aggregate.</para>
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<para>Images for ESXi use the VMDK format. You can convert
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QEMU disk images to VMDK, VMFS Flat Disks. These disk images
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can also be thin, thick, zeroed-thick, and eager-zeroed-thick.
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After exporting a VMFS thin disk from VMFS to the
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OpenStack Image service (a non-VMFS location), 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 since transfers
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require moving the full preallocated flat disk rather than the
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thin disk.</para>
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<para>The VMware host aggregate compute nodes communicate with
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vCenter rather than spawning directly on a hypervisor.
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The vCenter then requests scheduling for the instance to run on
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an ESXi hypervisor.</para>
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<para>This functionality requires that VMware Distributed Resource
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Scheduler (DRS) is enabled on a cluster and set to <guilabel>Fully
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Automated</guilabel>. The vSphere requires shared storage because the DRS
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uses vMotion, which is a service that relies on shared storage.</para>
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<para>This solution to the company's migration uses shared storage
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to provide Block Storage capabilities to the KVM instances while
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also providing vSphere storage. The new environment provides this
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storage functionality using a dedicated data network. The
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compute hosts should have dedicated NICs to support the
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dedicated data network. vSphere supports OpenStack Block Storage. This
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support gives storage from a VMFS datastore to an instance. For the
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financial company, Block Storage in their new architecture supports
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both hypervisors.</para>
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<para>OpenStack Networking provides network connectivity in this new
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architecture, with the VMware NSX plug-in driver configured. legacy
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networking (nova-network) supports both hypervisors in this new
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architecture example, but has limitations. Specifically, vSphere
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with legacy networking does not support security groups. The new
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architecture uses VMware NSX as a part of the design. When users launch an
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instance within either of the host aggregates, VMware NSX ensures the
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instance attaches to the appropriate network overlay-based logical
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networks.</para>
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<para>The architecture planning teams also consider OpenStack Compute
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integration. When running vSphere in an OpenStack environment, nova-compute
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communications with vCenter appear as a single large hypervisor. This
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hypervisor represents the entire ESXi cluster. Multiple nova-compute
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instances can represent multiple ESXi clusters. They can connect to
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multiple vCenter servers. If the process running nova-compute
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crashes it cuts the connection to the vCenter server. Any
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ESXi clusters will stop running, and you will not
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be able to provision further instances on the vCenter, even if you enable high
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availability. You must monitor the nova-compute service
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connected to vSphere carefully for any distruptions as a result of this
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failure point.</para>
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</section>
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