A logistics company expects its Amazon RDS cross-Region read replica to fail over synchronously, with no lag, when the primary Availability Zone is lost. What does that replica actually provide?
Select an answer to reveal the explanation.
Short Explanation
A photocopy in another city is not a live clutch between two engines. You are asking a cross-Region read replica to behave like a synchronous Multi-AZ standby, and it will not. Promotion is your step to take, and the copy can be behind the primary.
Full Explanation
Multi-AZ failover is synchronous replication to a standby in another Availability Zone of the same Region, and RDS fails over to that standby automatically. A cross-Region read replica replicates asynchronously, so it can lag the primary, and it becomes a writer only when you promote it. That promotion is a disaster-recovery step, not the Multi-AZ failover path. A second writer beside the primary is not what this replica provides; it stays read-only until promotion. Calling the replica a synchronous standby in the other Region reverses both the replication mode and who initiates the takeover. A query cache does not hold the database's durable storage and cannot accept writes when the primary volume fails. Caveat: promoting the replica while the old primary is still writable can split clients across two writers, so stop writes to the old primary before applications follow the new endpoint. Operational check: review replica lag before a drill, promote in a test environment, and confirm the application uses the promoted endpoint.