Help Center/ Document Database Service/ User Guide/ Instance Modifications/ Changing Replica Set Instance Nodes/ Adding Read Replicas to a Replica Set Instance
Updated on 2024-08-08 GMT+08:00
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Adding Read Replicas to a Replica Set Instance

Read replicas enhance read capabilities and reduce load on your instances. After a DDS replica set instance is created, you can create read replicas based on service requirements. To connect to a read replica, see Connecting to a Read Replica Using Mongo Shell.

Constraints

  • To use this function, contact customer service to apply for the required permission.
  • The version of a replica set instance must be 3.4, 4.0, or 4.2.
  • Nodes cannot be added to an instance that is being backed up.
  • An instance cannot be deleted when one or more nodes are being added.
  • When read replicas are being added, the DB instance may be intermittently disconnected once or twice for up to 30s each time.

Precautions

  • A maximum of five read replicas can be added to a replica set instance.

Procedure

  1. Log in to the management console.
  2. Click in the upper left corner and select a region and a project.
  3. Click in the upper left corner of the page and choose Databases > Document Database Service.
  4. On the Instances page, click the replica set instance.
  5. In the Node Information area on the Basic Information page, click Add Read Replicas.

    Figure 1 Creating read replicas

  6. On the Add Read Replicas page, specify Specifications, Node Class, Nodes, Parameter Template, and Delay, and click Next.

    Figure 2 Creating read replicas
    Table 1 Parameter description

    Parameter

    Description

    Read Replica Parameter Template

    The parameters that apply to the read replicas of a replica set instance. After a node are created, you can change the parameter template of the node to bring out the best performance.

    NOTE:

    Only whitelisted users can use this function. You need to submit a service ticket to apply for this function. In the upper right corner of the management console, choose Service Tickets > Create Service Ticket to submit a service ticket.

  7. On the displayed page, confirm the node configuration information.

    • 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 nodes.

  8. View the results.

    • When nodes are added, the status of the instance is Adding read replicas. The entire process takes about 15 minutes.
    • In the Node Information area, view the information about the nodes you added.
    • Choose More > View Delay in the Operation column to view the delay of the current node.