Upgrading vCenters with Enhanced Link Mode enabled over time vs rapid succession

Products

• VMware vCenter Server

Issue/Introduction

What are the impacts of upgrading vCenters over time vs in rapid succession?

Example: I would like to upgrade a single vCenter per day for a week.

Environment

VMware vCenter Server 7.0.x
VMware vCenter Server 8.0.x

Cause

Informational

Resolution

You can upgrade vCenters over time but the the sooner you can upgrade all vCenters in linked mode the better.  Here are some important points to consider:

• Actively running in a mixed mode is not a supported configuration (non upgrade issues caused by this might not be supported for example).  https://knowledge.broadcom.com/external/article?articleNumber=316078 
• To properly upgrade a cluster of VC's you'll need to shut them all down and take a snapshot of them before starting: https://knowledge.broadcom.com/external/article?articleNumber=313886.
  • This means that if you're into the process of upgrading over time and something goes wrong and you need to revert to snapshot, you must revert them all.
• vCenters that are on the upgraded versions cannot be managed by vCenters of a lower version.]
• You will see a warning banner during the mixed mode time frame.

Additional Information

Additional notes on upgrade can be found here: https://knowledge.broadcom.com/external/article?articleNumber=372863