Multi-AZ and Automated Backups
Enable Multi-AZ for synchronous standby replication and understand automated backup windows and retention periods.
What Is Multi-AZ on RDS?
Multi-AZ is an RDS high-availability feature that automatically provisions a synchronous standby replica in a different Availability Zone within the same Region. AWS manages the replication transparently—you connect using a single DNS endpoint and RDS routes traffic to the primary.
If the primary instance fails due to hardware, network, or OS issues, RDS performs an automatic failover to the standby in approximately 60–120 seconds. Your application reconnects using the same DNS endpoint, which now resolves to the standby's IP address.
Enabling Multi-AZ on an Existing Instance
You can enable Multi-AZ when creating an RDS instance or by modifying an existing one. When enabling on a running instance, AWS takes a snapshot of the primary, restores it in a second AZ, then synchronises using the engine's native replication. This process can cause brief I/O suspension on the primary, so schedule it during a low-traffic window or accept the maintenance window timing.
Multi-AZ is supported for all RDS engines including MySQL, PostgreSQL, MariaDB, Oracle, and SQL Server, and it does not require any application-level changes.
# Enable Multi-AZ on an existing RDS instance
aws rds modify-db-instance \
--db-instance-identifier mydb \
--multi-az \
--apply-immediatelyAll lessons in this course
- RDS Engines and Instance Classes
- Multi-AZ and Automated Backups
- Read Replicas for Read Scaling
- RDS Security: Encryption and Parameter Groups