# Setting up external replication from Multi-AZ DB clusters for Amazon RDS
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You can set up replication between a Multi-AZ DB cluster and a database that is external to Amazon RDS. 

External replication allows Multi-AZ DB clusters to replicate data between an RDS DB instance and an external database, either on-premises or in another cloud environment. It's beneficial for disaster recovery, data migration, and maintaining consistency between systems in different locations. The section covers the prerequisites for setting up replication, how to configure the process, and key considerations like replication latency, bandwidth, and compatibility with different database engines.

## RDS for MySQL
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To set up external replication for an RDS for MySQL Multi-AZ DB cluster, you must retain binary log files on the DB instances within the cluster for long enough to ensure that the changes are applied to the replica before Amazon RDS deletes the binlog file. To do so, configure binary log retention by calling the `mysql.rds_set_configuration` stored procedure and specifying the `binlog retention hours` parameter. For more information, see [binlog retention hours](mysql-stored-proc-configuring.md#mysql_rds_set_configuration-usage-notes.binlog-retention-hours).

The default value for `binlog retention hours` is `NULL`, which means that binary logs aren't retained (0 hours). If you want to set up external replication for a Multi-AZ DB cluster, you must set the parameter to a value other than `NULL`.

You can only configure binary log retention from the writer DB instance of the Multi-AZ DB cluster, and the setting is propagated to all reader DB instances asynchronously.

In addition, we highly recommend enabling GTID-based replication on your external replica. Then, if one of the DB instances fails, you can resume replication from another healthy DB instance within the cluster. For more information, see [Replication with Global Transaction Identifiers](https://dev.mysql.com/doc/refman/8.0/en/replication-gtids.html) in the MySQL documentation.

## RDS for PostgreSQL
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To set up external replication for an RDS for PostgreSQL Multi-AZ DB cluster, you must enable logical replication. For instructions, see [Setting up PostgreSQL logical replication with Multi-AZ DB clusters for Amazon RDS](USER_MultiAZDBCluster_LogicalRepl.md).