Read Replicas

A Read Replica is a read-only copy of a DBaaS instance. Applications can query it, and every write goes to the primary DBaaS instance. Adding a replica takes read traffic off the primary. A cross-region replica also keeps a copy of your data in the other region, and you can promote it into an independent DBaaS instance there. You promote a replica yourself, whenever you choose.

Region and network rules

A Read Replica can be in its primary’s region or in the other one, Delhi or Chennai. The primary needs SSL on before you add any Read Replica. A cross-region replica also needs an unencrypted primary, attached to a VPC with an active peering connection to the target region. Detaching the VPC pauses the sync until you reattach it, and deleting the peering connection ends the sync for good. If you want the replica as a DBaaS instance of its own, promote it before you change either; see Promote a Read Replica to Master Node.

Billing

You pay for each Read Replica separately, on top of the primary: at its plan’s hourly rate, or on its own committed plan. A replica is created on the primary’s plan, and a DBaaS instance can have up to four Read Replicas.

Stopping the primary leaves its replicas running and billing, and the stopped primary is billed too. To stop a replica’s charge, delete the replica.

Upgrading the primary’s plan resizes the primary. Existing replicas keep their old plan and its rate, and a replica you add after the upgrade gets the new plan.

Promotion

Promoting a Read Replica turns it into a new, independent DBaaS instance in the replica’s own region, which can differ from the primary’s. From then on, the new DBaaS instance is separate from the primary, and the split is permanent. See Promote a Read Replica to Master Node.