"Disconnecting" a managed host from vCenter Server: practical application?

[Jhel]

The vSphere client offers the possibility to "disconnect" a managed host from vCenter Server (rightclick > disconnect).

I was wondering in which situations this would be used/useful? Does it impact the VMs running on the host? Is "reconnecting" simply like initially connecting to a new host?

jhel

[f10]

Hi,

Firstly, disconnecting the ESXi host from vCenter will not affect any production VMs. Your VMs will continue to run however the VMs wont be able to utilize vCenter features like DRS, vMotion while the ESXi host is disconnected. I have done this in the past when the vpxa agent on the ESXi host is not updated, for e.g. you may see some state/orphaned VMs which you have already deleted.

Hope this helps !

-f10

[weinstein5]

And to add if the host is part of an DRS/HA cluster you will have to place it in maintenance mode and migrate any running VMs off of it -

[Jhel]

Ok, so the main purpose would be to "wipe&reinstall" the vpxa (vpxa gets installed at the moment you connect a host to vCenter Server ?) in case you suspect the communication between vCenter Server and an ESXi is somehow broken? Would that be a good interpretation?

jhel

[f10]

With the release of ESXi 5.0 the vpxa agents are now included in the base image and you dont have an option to unisntall/reinstall like you did in the previous versions. So the agents doesnt get uninstalled and reinstalled it remains in the image but get updated with the vCenter information. I have already shared some examples which would indicated a broken communication I cant think of any specific event where doing this would be mandatory or helpful.

[Jhel]

I'm sorry, a little bit confused here... Now you're saying disconnecting (and reconnecting) doesn't fix the imagined vpxa communication problem, or what? Still not sure then why the "disconnect" option even exists, certainly as readily available in the GUI like this???

jhel

[simon_wright · Accepted solution]

Here is what I use the disconnect button for:

I have an old vCenter 4 install with 10 ESXi 4.0 hosts, I have now built a vCenter 5.5 system and need to migrate to this vCenter but I cannot have any down time.

So I hit the disconnect button then add the ESXi 4.0 host into my new vCenter, then at my convenience I then vmotion of the 4.0 host onto a 5.5 host.

I hope this makes sense for you.

Simon.

[Jhel]

So essentially, because a host can only be managed by ONE instance of vCenter Server at a time, if you decide not to upgrade vSphere in-place (or can't for some reason) and set up an entirely new environment, a "disconnect" from the current vCenter Server and "connect" to the new one is the only way to get it "under the wings" of the new one?

Yes, that makes sense!

It's really rather meant for corner cases than anything else, then? Not something that is used regularly?