Which member of a high-availability cluster should be upgraded first in a Zero downtime upgrade?

Question

Quizplus · Accepted Answer

During the upgrade procedure, standby members are upgraded first. When upgrade on the final active member begins, the active member fails over to the standby member (or members, depending on the deployment: High Availability or Load Sharing). At this point, since connection tables between cluster members are not synced, all open connections are lost. Only a full connectivity upgrade (between minor versions) preserves open connections.

Which Member of a High-Availability Cluster Should Be Upgraded First