I received a call from a client asking for help removing maintenance mode from an ESXi host. The 5.5 host was put into maintenance mode, had some patches applied to it and when it came back to vCenter, the client was unable to exit Maintenance Mode. vCenter complained that the host was unavailable on the network or that the ‘Exit Maintenance Mode’ command was invalid for the specific state. Weird.
I connected to the ESXi Host directly from the VI client and the host showed it was NOT in Maintenance mode. Immediately that told me that the vCenter was not updating it’s status correctly. From the direct connection, I put the host back into Maintenance mode to match up what vCenter believed. At that point, I removed the ESXi host from the cluster and from vCenter and gave the Host a reboot. Freshen things up. Once returned it refused to be added back into the Cluster.
But then I remembered that pesky VMware KB 2140304 that states that ESXi hosts upgraded are not manageable by a vCenter of a lower patch version! The easiest fix for this is a quick patching of vCenter to the now current 5.5 Update 3e.
This was a blast from the past for me as most of my clients have upgraded to vSphere 6.x by now but for those out there still holding the line on 5.5, this was an easy one to fix. (Although be sure to always take a snapshot! - Damn you Murphy!)