It is common to run vCenter as a virtual machine. When the VM runs inside a vSphere cluster with DRS enabled configured to automatically migrate virtual machines you might loose track of where the vCenter-VM is running. When you need to troubleshoot the vCenter VM you might need to use the vSphere Client to manage that VM, but on which cluster node does the VM run? Therefor it might be a good idea to always run the vCenter VM on the same ESXi host.
To do this you must first create a VM DRS Group (containing the vCenter VM) and a Host DRS Group (containing the ESXi-host to run the VM on). The screenshot below shows these two groups.
When the groups have been created click Add and add the VM and ESXi host to the two groups.
Once the two groups have been created it is time to create the rule. In the DRS rules window click Add and define a rule as in the screenshot below. Make sure to use the Should run on hosts in this group rule and not a Must run-rule. Because in that case the VM would not come on-line after a HA-failover. With the Should run-rule the VM can be started by HA on another host in case of a failure.
When the rule is created and enabled it should look like this: