Updated on 2022-08-16 GMT+08:00

Creating a Read Replica

Scenarios

Read replicas are used to enhance the read capabilities and reduce the load on primary DB instances.

After a DB instance has been created, you can create read replicas for it.

A maximum of five read replicas can be created for a primary DB instance.

Only RDS for SQL Server 2019 Enterprise Edition and 2017 Enterprise Edition support read replicas.

Procedure

  1. Log in to the management console.
  2. Click in the upper left corner and select a region and a project.
  3. Click Service List. Under Database, click Relational Database Service. The RDS console is displayed.
  4. On the Instance Management page, locate the target DB instance and choose More > Create Read Replica in the Operation column.

    Alternatively, click the target DB instance. In the DB instance topology, click under the primary DB instance to create read replicas.

  5. On the displayed page, configure information about the DB instance and click Next.

    Table 1 Basic information

    Parameter

    Description

    Region

    By default, read replicas are in the same region as the primary DB instance.

    DB Instance Name

    Must start with a letter and consist of 4 to 64 characters. It can contain only uppercase letters, lowercase letters, digits, hyphens (-), and underscores (_).

    DB Engine

    Same as the DB engine of the primary DB instance by default and cannot be changed.

    DB Engine Version

    Same as the DB engine version of the primary DB instance by default and cannot be changed.

    AZ

    RDS allows you to deploy primary DB instances and read replicas in a single AZ or across AZs to improve reliability.

    Table 2 Instance specifications

    Parameter

    Description

    Instance Class

    Refers to the CPU and memory of a DB instance. Different instance classes have different numbers of database connections and maximum IOPS.

    For details about instance classes, see DB Instance Classes.

    After a DB instance is created, you can change its CPU and memory. For details, see Changing a DB Instance Class.

    Storage Type

    Determines the DB instance read/write speed. The higher the maximum throughput is, the higher the DB instance read/write speed can be.

    • High I/O: supports a maximum throughput of 150 MB/s.
    • Ultra-high I/O: supports a maximum throughput of 350 MB/s.

    Storage Space

    Contains the file system overhead required for inode, reserved block, and database operation.

    By default, storage space of a read replica is the same as that of the primary DB instance.

    Table 3 Network

    Parameter

    Description

    VPC

    Same as the primary DB instance's VPC.

    Subnet

    Same as the primary DB instance's subnet. A floating IP address is automatically assigned when you create a read replica. You can also enter an unused floating IP address in the subnet CIDR block. After the read replica is created, the floating IP address cannot be changed.

    Security Group

    Same as the primary DB instance's VPC.

  6. Confirm specifications.

    • If you need to modify your settings, click Previous.
    • Otherwise, click Submit.

  7. After a read replica has been created, you can view and manage it on the Instance Management page by clicking on the left of the DB instance to which it belongs.

    Alternatively, click the target DB instance. In the DB instance topology, click the target read replica. You can view and manage it in the displayed pane.

Follow-up Operations

Managing a Read Replica