Scenarios

DDS allows you to scale the three-node replica set instances up to five-node or even seven-node architecture. All new nodes are secondary nodes and support primary/secondary switchovers, improving data reliability.

Constraints

• You can add nodes when the instance status is Available, Deleting backup, or Checking restoration.
• A DB instance cannot be deleted when one or more nodes are being added.
• After a node is added, data is continuously synchronized to the secondary node. The new connection address configured for your application may take effect only after the application is restarted. To ensure high availability of the connection, you need to activate the newly added node. Then, the new node can participate in the primary/secondary switchover.
• Nodes cannot be manually deleted.
• If you use a three-node, five-node, or seven-node replica set backup to restore data to a new DB instance, the new DB instance uses the three-node replica set architecture.

Procedure

1. Log in to the DDS console.
2. On the Instance Management page, click the target replica set instance.
3. In the Node Information area on the Basic Information page, click Add Secondary Node.
4. Specify Quantity and click Next.
   Figure 1 Adding secondary nodes
   

   You can add five or seven nodes.

5. On the displayed page, confirm the node configuration information.
   • Yearly/Monthly
     • If you need to modify your settings, click Previous to go back to the page for you to specify details.
     • If you do not need to modify your settings, click Submit to go to the payment page and complete the payment.
   • Pay-per-use
     • If you need to modify your settings, click Previous to go back to the page for you to specify details.
     • If you do not need to modify your settings, click Submit to add the nodes.

6. View the result of adding nodes.
   • The status of the DB instance in the instance list is Adding node.
   • In the Node Information area, view the information about the nodes you added.
   Figure 2 Node information
   

7. In the Node Information area, click Activate Secondary Node so that the new secondary node can participate in the primary/secondary switchover.
   

   During the primary/secondary switchover, the replica set randomly selects a secondary node as the primary node. Ensure that you have modified the connection address of your application.