When you upgrade vCenter Server, you can upgrade the Auto Deploy Server at the same time. If you postpone the update, problems with the vSphere HA agent might result.
When you upgrade vCenter Server, vCenter Server replaces the vSphere HA agent (vmware-fdm) version 5.0 with vSphere HA agent version 5.1 or later on each ESXi host. On hosts provisioned with Auto Deploy, the replacement is not permanent because no state is on the host. If vCenter Server is not available, the ESXi hosts do not have the correct vSphere HA agent and cannot join a cluster.
The Auto Deploy 5.0 server does not automatically upgrade the FDM VIB to version 5.1 or later. Unless you create a new image that includes the VIB, Auto Deploy reverts to the FDM VIB version 5.0 after reboot.
Upgrade the Auto Deploy server.
If you cannot upgrade the Auto Deploy server, you can use Image Builder PowerCLI cmdlets included with vSphere PowerCLI to create an ESXi 5.0 image profile that includes the new vmware-fdm VIB. You can supply your hosts with that image profile.
At the PowerCLI prompt, add the ESXi 5.0 software depot and add the software depot that contains the new vmware-fdm VIB.
Add-EsxSoftwareDepot C:\Path\VMware-Esxi-5.0.0-buildnumber-depot.zip Add-EsxSoftwareDepot http://vcenter_server/vSphere-HA-depot
Create a rule that assigns the new image profile to your hosts, and add the rule to the ruleset.
New-DeployRule -Name "Rule Name" -Item "ImageName" -Pattern "my host pattern" Add-DeployRule -DeployRule "Rule Name"
Perform a test-and-repair compliance operation for the hosts to permanently include the vSphere HA agent on the hosts.
$result = Test-DeployRuleSetCompliance Host_list Repair-DeployRuleSetCompliance -TestResult $result