A recent issue we experienced was seeing hosts disconnecting from vCenter and reconnecting. The host would drop and randomly come back for about an hour or more. The VM’s never saw any issues nor was there any type of outage. It was that vCenter could no longer see the host.
After quite a bit of troubleshooting, I started digging around in the vCenter Server Settings (Administration > vCenter Server Settings). In this menu, there is a tab for Runtime settings. I noticed that we only had the vCenter Server Name filled in and not the vCenter Server Managed IP. The window looks as follows:
After completing all the fields in this window, the hosts magically all reconnected and have not dropped again. This is due to the fact that the hosts use these settings to check in with the vCenter box and they let the host know who it’s being managed by. As you can guess, if the host doesn’t know who’s managing it, it doesn’t know who to check in with.
The more curious issue was that this field hadn’t even been filled out, but didn’t start immediately. Which made troubleshooting more difficult and made us all panic as we started getting numerous alerts for hosts dropping.
As best practice, whether you only have 1 vCenter server, is to fill out all these fields and enure they are correct. Especially if you want the host to check in with the correct vCenter server and you don’t want the heart attack of seeing numerous hosts suddenly disconnecting from vCenter.