DB Instance Replication
Currently, you can create replicas of your DB instances in two ways. All DB instances can have a Multi-AZ deployment, where Amazon RDS automatically provisions and manages a standby replica in a different Availability Zone (independent infrastructure in a physically separate location). In the event of planned database maintenance, DB instance failure, or an Availability Zone failure, Amazon RDS will automatically failover to the standby so that database operations can resume quickly without administrative intervention. For more information on Multi-AZ deployments, see High Availability (Multi-AZ).
Amazon RDS also uses the PostgreSQL, MySQL, and MariaDB DB engines' built-in replication functionality to create a special type of DB instance called a Read Replica from a source DB instance. Updates made to the source DB instance are asynchronously copied to the Read Replica. You can reduce the load on your source DB instance by routing read queries from your applications to the Read Replica. Read Replicas allow you to elastically scale out beyond the capacity constraints of a single DB instance for read-heavy database workloads. For more information about Read Replicas, see Working with PostgreSQL, MySQL, and MariaDB Read Replicas