Creating a Read Replica

Scenarios

Read replicas of a DB instance are used to enhance instance capabilities and reduce the read pressure on the primary node. After a DB instance is created, you can create read replicas for it.

There are synchronous and asynchronous read replicas.

• Synchronous read replicas: Their failover priority is 1 and specifications are the same as those of the primary node. To avoid failover failures caused by inconsistent specifications between the primary node and read replicas, a DB instance must have a synchronous read replica, and a multi-AZ DB instance must have a synchronous read replica in a different AZ from the primary node.
• Asynchronous read replicas: Their failover priority is not 1 and specifications are different from those of the primary node.

For more information about read replicas, see Introducing Read Replicas.

Deployment Relationships Between the Primary Node and Read Replicas

Constraints

• You can create a maximum of 15 read replicas.
• If all synchronous read replicas are unavailable during a failover, an asynchronous read replica will be promoted to primary.

Procedure

1. Log in to the management console.
2. Click in the upper left corner and select a region and project.
3. Click in the upper left corner of the page, choose Database > TaurusDB.
4. On the Instances page, locate the instance you want to add read replicas to and choose More > Create Read Replica in the Operation column.
5. On the displayed page, set required parameters.

   Table 1 Parameter description

   Parameter	Description
   Billing Mode	Pay-per-use DB instance: Pay-per-use read replicas can be added. Yearly/Monthly DB instance: Yearly/Monthly and pay-per-use read replicas can be added.
   Failover Priority	Failover priority ranges from 1 for the first priority to 16 for the last priority. This priority determines the order in which read replicas are promoted when recovering from a primary node failure. Read replicas with the same priority have a same probability of being promoted to the new primary node. You can configure a failover priority for up to 9 read replicas, and the default priority for the remaining read replicas is -1, indicating these read replicas cannot be promoted to primary. You can change the failover priority of a read replica.
   AZ	TaurusDB multi-AZ instances allow you to select an AZ when creating a read replica. If no AZs are specified, the created read replicas are evenly distributed in each AZ. If too many nodes are created in a specified AZ, the read replicas may fail to be created due to insufficient resources.
   Instance Specifications	This parameter is only available for cluster instances. If the failover priority is set to 1, the specifications of read replicas must be the same as those of the primary node.
   Quantity	You can create up to 15 read replicas for a yearly/monthly or pay-per-use DB instance. You can contact customer service to create up to 7 read replicas for a serverless DB instance.

6. For a yearly/monthly instance, click Next and select a payment mode.
7. For a pay-per-use or serverless instance, click Next.
8. Check the read replica settings.
   • If you need to modify the settings, click Previous.
   • If you do not need to modify the settings, click Submit.

9. View the new read replica information in the Node List area of the Basic Information page. You can also promote a read replica to primary or delete a read replica.