You might be wondering why the need to add a dvd drive to a VM running vCenter in the first place.
Well, I recently had to upgrade a vCenter Server Appliance (VCSA) from version 6.5 to 6.5 U1e for a customer by using the offline bundle rather than the online method. This is why I needed to add a dvd drive to the vCenter VM and then mount the VCSA update ISO file. Everything went just fine and my VCSA was up to date and running after a couple of minutes and a reboot.
The thing is that I didn’t immediately un-mount the ISO file and remove the dvd drive from the vCenter VM after the upgrade ; and a few days later I had to configure VCHA (vCenter High Availability) which allow to have a passive vCenter to go online in case of failure of the active node. I won’t go into further details as this is not the topic today.