Troubleshooting VMware High Availability (HA)

Please read the following articles from VMware:
Troubleshooting VMware High Availability
Verifying and reinstalling the correct version of the VirtualCenter Server agents

Especially for ESXi use the following procedure to reinstall VirtualCenter HA agents:
 To determine the version and build number of your VirtualCenter installation, click Help > About from within VirtualCenter.
Right-click on the ESXi host and click Disconnect to disconnect the ESXi host from VirtualCenter.
Log in to ESXi Troubleshooting Mode.
Run the following command to determine the version of the VirtualCenter agent (vpxa) that is installed:

cat `ls -t /var/log/vmware/vpx/vpxa*` | head -1

The output appears similar to:

Log for VMware VirtualCenter Agent, pid=1976, version=2.5.0, build=build-147633, option=Release, section=394

Ensure that the output matches the information from first step. If the versions do not match, reinstall the agents.

Reinstalling the ESX host management agents and HA agents on ESXi

• Right-click on the ESXi host and click Disconnect.  This disconnects the ESXi host from the VirtualCenter Inventory.
• Log in to ESXi Troubleshooting Mode.Uninstall the vpxa and aam components from the VMware ESXi host using the following commands:

/opt/vmware/uninstallers/VMware-vpxa-uninstall.sh
/opt/vmware/uninstallers/VMware-aam-ha-uninstall.sh

• Right-click on the ESXi host and click Connect. This initiates a re-install of the vpxa agent.
• Add the host to the appropriate cluster. This initiates a re-install of the aam agent. 

If the agent fails to automatically install when connecting the ESX host in the vCenter Server:
Verify that /tmp/vmware-root exists on the ESX host. vCenter stages the vpxa RPM in this folder. To add this directory, execute:

mkdir -p /tmp/vmware-root