An external replica is a method that allows you to create a read-only copy of your Cloud SQL instance on an external server, such as a Compute Engine instance or an on-premises database server1. An external replica can help you scale reads and offload management operations from your data center to Google Cloud. You can also use an external replica for disaster recovery, migration, or reporting purposes1.
To create an external replica, you need to configure a Cloud SQL instance that replicates to one or more replicas external to Cloud SQL, and a source representation instance that represents the source database server in Cloud SQL1. You also need to enable access on the Cloud SQL instance for the IP address of the external replica, create a replication user, and export and import the data from the source database server to the external replica1.