DRS rules fail to enable and switch immediately back to not enabled

Products

• VMware vCenter Server

Issue/Introduction

• You are trying to enable an existing or newly created DRS rule (for example a Host to VM affinity rule).
• Multiple other existing rules in the same cluster.
• After changing the rule status to enabled, and leaving the wizard, it immediately goes back to being disabled.

Environment

8.x

Cause

This issue is caused by one or more of the existing rules having invalid (aka null) entries. These can be caused by either virtual machines or hosts referenced in them, which have been removed from the vCenter inventory.

The references for these objects can get stuck in the affinity rule, making it invalid.

Resolution

To fix the issue:

1. Review the existing affinity/DRS rules under VM/Host Rules in the Configure tab for the cluster and check all existing rules for any showing "null" entries under the VM's configured.
2. Remove these entries or remove the related rule completely.
3. Proceed to Enable the rule that would not Enable previously.