Amazon RDS Multi-AZ: High Availability and Failover

Amazon RDS Multi-AZ is designed to improve database availability and resilience.

RDS maintains a standby database in a different Availability Zone and synchronously replicates changes from the primary. If the primary becomes unavailable, RDS can automatically fail over to the standby.

Simple mental model

Multi-AZ → "What if my database fails?"
Read Replica → "What if I have too many reads?"

With RDS Multi-AZ, you generally don't switch between primary and standby in the application. RDS handles the failover behind the endpoint, and the application reconnects to the same endpoint.