After you migrate your data to a Cloud SQL destination instance, with
Database Migration Service, you can set up cascading read replicas for your destination
instance.
[Cascading read replicas](https://docs.cloud.google.com/sql/docs/postgres/replication.md.txt#cascading-replicas) let you create a read replica under a
Cloud SQL read replica in the same or different region before promoting your
instance to primary. You can add up to four levels of cascading read replicas,
including the primary instance.

## Set up cascading read replicas

To migrate your data to a Cloud SQL destination that is using cascading read
replicas:

1. Perform the standard migration process, but don't promote the migration job
   when it reaches the CDC phase. For more information, see
   [Get started with homogeneous PostgreSQL migrations](https://docs.cloud.google.com/database-migration/docs/postgres/get-started-with-postgres-migrations.md.txt).

2. Once in the CDC phase, you can set up your cascading read replica. For
   information about how to create cascading read replicas for a Cloud SQL destination
   instance, see
   [Set up a cascading replica](https://docs.cloud.google.com/sql/docs/postgres/replication/configure-replication-from-external.md.txt#set_up_a_cascading_replica).

3. You can promote your Cloud SQL replica to a primary instance using Database Migration Service.
   For information about promoting a destination instance, see
   [Promote a migration](https://docs.cloud.google.com/database-migration/docs/postgres/promote-migration.md.txt).

When you promote the Cloud SQL replica to a primary instance, the replica's
cascading replica hierarchy is retained.

## What's next

To get a complete, step-by-step migration walkthrough, see
[Get started with Cloud SQL for PostgreSQL migrations](https://docs.cloud.google.com/database-migration/docs/postgres/get-started-with-postgres-migrations.md.txt).