I have an azure SQL database configured with 400 DTUs that is replicated to another SQL Server database in a different region for failover. I'd like to save some money (and live with a lag on failover) by lowering the DTU's on the secondary database but I am worried that doing this could cause performance issues in my primary database if the secondary one maxes out on DTU's.
Does the secondary database maxing out on DTU's affect the primary or does the replication just catch up eventually?
You should be cautious having the secondary database at a lower performance level than the primary as you need to ensure it has enough capacity to handle the update workload on the primary, otherwise transactions will be queued up for replication and you could lose significant amounts of data in the case of a forced failover.
The published RPO = 5 sec cannot be guaranteed unless the secondary database is configured with the same compute size as the primary. For more information please read this documentation.
