Error: "<host> has an unknown health state." when Proactive HA is enabled on a cluster

Products

• VMware vCenter Server

Issue/Introduction

• Proactive HA is enabled on a cluster
• 'All Issues' in vCenter displays a Configuration Issue "<host> has an unknown health state."
• This message is unable to be 'Acknowledged' or 'Reset to Green'
• There may be VM migrations after enabling Proactive HA or after restarting vCenter Server services.

Environment

VMware vCenter Server 7.x
VMware vCenter Server 8.x

Cause

• After Proactive HA is enabled on a cluster, or after restarting vCenter Server services with Proactive HA enabled on a cluster, the hosts in the cluster have an initial Proactive HA health state of “unknown” until the third party health provider posts the next health updates.
• Distributed Resource Scheduler (DRS) treats hosts with “unknown” health state as “Quarantined” hosts, and therefore tries to avoid placing VMs on them if possible.
• If DRS load balancing happens before all hosts in the cluster receive their health updates, VMs on hosts with an “unknown” health state could be migrated to other hosts with a “green” health state.

Resolution

This behavior is expected with the current design.

To avoid such VM migrations:

• set DRS to manual mode before restarting vCenter Server or enabling Proactive HA on a cluster.
• set it back to Fully Automated after all hosts receive at least one health update (host no longer has the “unknown health state” config issue).

To clear the message from 'All Issues':

• disable and re-enable Proactive HA on the cluster.  

Additional Information

See Configure Proactive HA.