# Amazon RDS on AWS Outposts Read Replicas
Amazon RDS Read Replicas provide enhanced performance and durability for Amazon RDS database (DB) instances. They make it easy to elastically scale out beyond the capacity constraints of a single DB instance for read-heavy database workloads. Amazon RDS on AWS Outposts uses the MySQL and PostgreSQL DB engines' built-in replication functionality to create a read replica from a source DB instance. The source DB instance becomes the primary DB instance. Updates made to the primary DB instance are asynchronously copied to the read replica. Read replica use Customer-owned IP (CoIP) model and the replications runs on your local network.
## Considerations for Amazon RDS on Outposts Read Replicas
Review the following considerations for Amazon RDS on Outposts deployments for Read Replicas:
+ You can't create read replicas for RDS for SQL Server on RDS on Outposts DB instances.
+ Cross-Region read replicas aren't supported on RDS on Outposts.
+ Cascading read replicas aren't supported on RDS on Outposts.
+ The source RDS on Outposts DB instance can't have local backups. The backup target for the source DB instance must be your AWS Region. Ensure you have a redundant [service link connection](https://docs.aws.amazon.com/outposts/latest/userguide/region-connectivity.html) of at least 500 mbps to send your RDS backups to AWS Region databases with frequently changing data or heavy write traffic.
+ Read replicas require customer-owned IP (CoIP) pools.
+ Read replicas on RDS on Outposts can only be created in the same virtual private cloud (VPC) as the source DB instance.
+ Read replicas on RDS on Outposts can be located on the same Outpost or another Outpost in the same VPC as the source DB instance.
+ You can't create read replicas for DB instances encrypted with AWS KMS External Key Store (XKS).
+ Creating your read replica as a Multi-AZ DB instance is independent of whether the source database is a Multi-AZ DB instance.