You can create read-only instances to process massive read requests sent to the database and increase the application throughput. A read-only instance is a read-only copy of the master instance. Changes to the master instance are also automatically synchronized to all relevant read-only instances through the native replication capability of MySQL.


  • Currently the following instances support read-only instances:
    • MySQL 5.7 High-Availability Edition (based on local SSDs)
    • MySQL 5.6
    • SQL Server 2017
  • Quantity of read-only instances
    Database type Memory Max number of read-only instances
    MySQL ≥ 64 GB 10
    < 64 GB 5
    SQL Server Any 7
  • Read-only instance is subject to an additional charge and its billing method is Pay-As-You-Go. For more information, see Pricing for read-only instances.
  • The read-only instance automatically copies the whitelist its master instance, but the whitelist of the read-only instance and that of the master instance are independent. To modify the whitelist of the read-only instance, see Set a whitelist.


  1. Log on to the RDS console.
  2. Select the region where the target instance is located.
  3. Click the ID of the target instance to visit the Basic Information page.
  4. In the Instance Distribution area, click Add Read-only Instance, as shown in the following figure.

  5. On the purchasing page, choose the configuration of the read-only instance, and then click Buy Now.
    • We recommend that the read-only instance and the master instance be in the same VPC.
    • To guarantee sufficient I/O for data synchronization, we recommend that the configuration of the read-only instance (the memory) is not less than that of the master instance.
    • We recommend that you purchase multiple read-only instances to improve availability.
  6. Select Product Terms of Service and Service Level Notice and Terms of Use, and then click Pay Now.
  7. After creating the read-only instance, you can view it on the Instances page, as shown in the following figure.