This topic provides an overview of read-only instances in RDS for MySQL. You can create one or more read-only instances to support a massive number of read requests and increase the throughput of applications.

Background information

An RDS for MySQL read-only instance is a read-only copy of the corresponding master instance. Changes to the master instance are automatically replicated to all corresponding read-only instances. You can set the replication delay in each read-only instance.

Note
  • Currently the following MySQL versions and RDS editions support read-only instances:
    • MySQL 8.0 High-availability Edition (with local SSDs)
    • MySQL 5.7 High-availability Edition (with local SSDs)
    • MySQL 5.6
  • Each read-only instance adopts a single-node architecture (that is, without slave nodes).

Pricing

Read-only instances are billed by using the pay-as-you-go billing method. For more information, see ApsaraDB RDS for MySQL pricing.

Features

Read-only instances in RDS for MySQL offer the following features:

  • A read-only instance is located in the same or different zones from its corresponding master instance.
  • The specifications of a read-only instance do not need to be the same as that of the corresponding master instance and can be changed at any time. We recommend that the specifications of a read-only instance be greater than or equal to that of the corresponding master instance. If the specifications of a read-only instance is lower than that of the corresponding master instance, the read-only instance may suffer from high delay or load.
  • The network type of a read-only instance can be different from that of its corresponding master instance.
  • No account or database maintenance is required for a read-only instance. Both accounts and databases are replicated from the corresponding master instance.
  • When you create a read-only instance, the system automatically replicates the whitelists of the corresponding master instance. After a read-only instance is created, its whitelists are independent of the whitelists of the corresponding master instance. If you want to change the whitelists of the read-only instance, see Configure a whitelist for an RDS for MySQL instance.
  • Read-only instances support monitoring and alerting. Specifically, up to 20 performance metrics, including the disk capacity, IOPS, number of connections, CPU utilization, and network traffic.

Limits

  • The number of read-only instances that a master instance can have varies depending on its memory size.
    Database type Memory Max number of read-only instances
    MySQL ≥ 64 GB 10
    < 64 GB 5
  • Read-only instances do not support backup settings or manual backups.
  • Read-only instances do not support the creation of temporary instances through backup files or backups, or support the overwriting of instances by using backup sets.
  • After a read-only instance is created, the master instance does not support data recovery through the direct overwriting of instances by using backup sets.
  • You cannot migrate data to read-only instances.
  • You cannot create or delete databases for read-only instances.
  • You cannot create or delete accounts for read-only instances.
  • You cannot authorize accounts or change account passwords for read-only instances.

FAQ

Can the accounts on the master instance be used on the read-only instances attached with it?

Accounts on the master instance are replicated to the read-only instances. You can use the accounts to read data from the read-only instances but cannot write data into the read-only instances.