We are doing way more master switchovers and part of the switchover is the replicas topology changes. Basically move all of the replicas (except the-to-be-master) under the-to-be-master. For example:
(and during the actual switchover, you just bring the old master under the new one)
This happens around half an hour before the actual switchover (taking around ten to twenty minutes) and only deals with replicas. Yet MediaWiki is acting too smart and decides to go read-only a lot during that time, causing read-only errors way more than the actual switchover: https://logstash.wikimedia.org/goto/580e0362614b1ffd4df5d71749a681a6
This needs fixing.