vCenter Server on VM Quick Tip: Use VM-Host Affinity Rules

This is not really a new tip, but I have been coming across so many customers lately that either are not virtualizing vCenter because they have had a bad experience or because they believe that this is a core infrastructure piece that needs to remain outside of the virtual environment it manages. I am of the opinion that vCenter should be virtualized and that there is only goodness that comes out of virtualizing vCenter server. That being said, like with everything in life, doing it right makes all the difference in the world.

A customer who was about to migrate vCenter back to a physical machine had an outage and did not know which ESXi host the vCenter was running. From that, they arrived at the conclusion that it was far too risky to continue.

After a bit of conversation I convinced them of all the benefits of keeping vCenter virtualized as long as some basic best practices were taken into consideration. To address their issues, I suggested that they set up a VM-Host Affinity rule. What that allows them to do is to pin vCenter on to a set of ESXi hosts so that it can continue to participate in DRS balancing and all the other benefits, but it can only vMotion among the ESXi hosts that they specify.

How is this beneficial? In the event that they should have another outage, they will immediately know that vCenter resides on one of the ESXi hosts that they specified in the VM-Host Affinity rule. One of the other recommendations that I gave them is since they were using blade servers, I suggested that the hosts that they pick to participate in the support of vCenter Server should not be on the same physical chassis. In other words, pick ESXi hosts from different chassis will limit your exposure a bit more.

Now, I know some of you will say that we can prevent vCenter server from participating in DRS altogether and just pin it to one ESXi host. That definitely works, but I would recommend the more elegant solution of letting vCenter partake in all the benefits of DRS and specifying the hosts to which it can move -- simple enough, right?

This is just one of many best practices around vCenter Server as a VM,, but what I wanted to leave you with is that vCenter can and should absolutely be virtualized and reap the benefits that virtualization presents.

Posted by Elias Khnaser on 06/30/2014 at 9:35 AM