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Read Replicas

  • A multi-AZ instance can not be promoted to a read-replica.
  • There is no charge for primary-to-secondary data replication.
  • Although it’s not particularly common, you can set up a read replica in an on-premises instance. Additionally, read replicas are often created in separate regions from the primary instance, to improve performance for clients closer to different regions than the primary instance.
  • Currently, read replicas in RDS are only supported by MariaDB, MySQL, and PostgreSQL. Not for DynamoDB
  • Read replicas are updated via asynchronous replication— the most performant approach.
  • Read replica setup only allows for five read replicas. This is not a limit that can be raised by AWS.
  • Read replica has its own database engine active so that it can be promoted to a primary DB.


  • Multi-AZ setup is focused on disaster recovery and fault tolerance, while read replicas provide performance and scalability.
  • You can manually promote (not automatically ) a read replica instance to a stand-alone instance if you have to.
  • Read replicas do not create automatic backups, but the primary database instance must have automatic backups enabled to create read replicas.
  • There is no particular performance increase in a Multi-AZ deployment unless read replicas are also turned on.

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