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