If I wanted to, this could be a very big post all about configuring HA correctly. But I don’t want to reinvent the wheel. Instead I just want to share my experiences with this error:

HA Agent on ESX-HOST in cluster CLUSTER-NAME has an error

Odds are that you will eventually see this one pop up in vCenter for one of your ESX 3.x hosts. If you’re not sure what it means, well the translation basically is that the host displaying the error could fail and your VMs running on it probably won’t get started up automatically on another host. Essentially HA is broken on the host. More >