This document describes how to prepare for a vCenter version upgrade and the downtime during upgrade.
Disable auto-repair
Before the vCenter upgrade,
disable autoRepair
on all user and admin clusters. This prevents machines from being recreated
while vCenter is unavailable.
Downtime during vCenter upgrade
There shouldn't be any downtime for the admin cluster and user clusters running in the vCenter during upgrade. The clusters remain up the entire time. However, there will be downtime for vCenter services like vMotion/DRS and VM creation.
If your workload directly interacts with vCenter, it might have downtime during the vCenter upgrade due to the vCenter service unavailabilities.
Major version upgrade
To upgrade vCenter to the next major version, a new Virtual Center Appliance will be deployed. And then all vCenter services are shutdown while it copies all data to the new appliance. Once the data is copied, the new appliance reboots and takes over the identity (hostname/IP/etc) of the old vCenter.
Major version have been seen to have about 30 mins of downtime for the vCenter API.
Minor version upgrade
The minor version upgrade will just update packages inside the OS and then reboot the appliance, which takes shorter time than major upgrade.
For minor updates, we have seen a downtime around 5 mins for the vCenter API.
Known Issue
Machines might go to Unavailable state after a vCenter reboot for versions
< 7.0U2. More details see the known issue.