Does RDS Support Cross-AZ High Availability?

Yes. When you create a DB instance, you can select Primary/Standby for DB Instance Type and then select different AZs for Primary AZ and Standby AZ.

RDS does not support 3-AZ deployment.

An AZ is a physical region where resources have independent power supplies and networks. AZs are physically isolated but interconnected through an internal network.

RDS allows you to deploy primary/standby DB instances in an AZ or across AZs. You can determine whether the standby AZ is the same as the primary AZ.

• If they are different (default setting), the primary and standby instances are deployed in different AZs to ensure failover support and high availability.
• If they are the same, the primary and standby instances are deployed in the same AZ. If an AZ failure occurs, high availability cannot be ensured.