In VMWare world administrators/ O&M team uses VM placement policy to define the placement of a virtual machine on a host or group of hosts. It is a mechanism for cloud provider administrators/operation teams to create a named group of hosts within a provider VDC. The named group of hosts is a subset of hosts within the provider VDC clusters that might be selected based on any criteria such as performance tiers or licensing.
Recently Microsoft announced the similar/same Placement policies to define constraints for running virtual machines in the Azure VMware Solution Software-Defined Data Center (SDDC). These feature allow to decide where and how the virtual machines should run within the SDDC clusters.
With this function when the admin / O&M team create a placement policy, it creates a vSphere Distributed Resource Scheduler (DRS) rule in the specified vSphere cluster which is deployed in the Azure VMware Solution . It also includes additional logic for interoperability with Azure VMware Solution operations.
There are two basic placement policy types now supported as part of the General availability:
- Virtual Machine to Virtual Machine: this refers to a policy that is applied to VMs with respect to each other.
- VM-VM Affinity policies instruct DRS to try keeping the specified VMs together on the same host for performance reasons as an example.
- VM-VM Anti-Affinity policies instruct DRS to try keeping the specified VMs apart from each other on separate hosts. It’s useful in scenarios where you may want to spread your virtual machines across hosts to ensure availability of the applications.
- Virtual Machine to SDDC Host: this refers to a policy applied to selected VMs to either run on, or avoid selected hosts.
- VM-Host Affinity policies instruct DRS to try running the specified VMs on the hosts defined.
- VM-Host Anti-Affinity policies instruct DRS to try running the specified VMs on hosts other than those defined.
In addition to the above , Azure VMware Solution now lets you restrict vMotions of selected VMs through a policy called “Restrict VM movement”. When enabled, vSphere DRS will not automatically vMotion a virtual machine from a host it currently resides on. This can be useful for workloads that are vMotion sensitive. Additional documentation is available on this link
