This topic provides an overview of the read-only instances of ApsaraDB RDS for MySQL. If a large number of read requests overwhelm the primary instance, your business may be interrupted. In this situation, you can add one or more read-only instances to offload read requests from the primary instance and increase the throughput of your application.

For information about read-only instances in other database engines, see the following topics:

Background information

ApsaraDB RDS for MySQL replicates data from the secondary instance to every read-only instance you create. After data on the primary instance is updated, the updated data is replicated to each read-only instance. You can set a replication delay for a read-only instance. For more information, see Set a replication delay for an RDS MySQL read-only instance.

Note Each read-only instance works in a primary/secondary architecture to ensure high availability.

Prerequisites

The instance runs one of the following MySQL versions and RDS editions:

  • MySQL 8.0 in the High-availability Edition or Enterprise Edition
  • MySQL 5.7 in the High-availability Edition or Enterprise Edition
  • MySQL 5.6
Note If your instance running MySQL 5.7 in the Enterprise Edition does not support read-only instances, submit a ticket.

Billing

Payment method: pay-as-you-go or subscription. For detailed pricing, please refer to the web console when creating a read-only instance.

Features

  • Read-only instances support pay-as-you-go for flexible billing and subscription for lower costs.
  • Read-only instances reside in the same region as the primary instance, but possibly in different zones.
  • The specifications of a read-only instance can differ from the specifications of the primary instance, and can be changed at any time. We recommend that the specifications of a read-only instance be greater than or equal to the specifications of the primary instance. If the specifications of a read-only instance are lower than the specifications of the primary instance, the read-only instance may encounter high latency or be unable to handle heavy loads.
  • The network type of a read-only instance can differ from that of the primary instance.
  • Read-only instances do not require database or account maintenance, because their database and account information is synchronized with the primary instance.
  • ApsaraDB RDS for MySQL automatically replicates the whitelists of the primary instance to every read-only instance you create. After a read-only instance is created, its whitelists are independent of the whitelists configured on the primary instance. For information about how to modify the whitelists of a read-only instance, see Configure a whitelist for an ApsaraDB RDS for MySQL instance.
  • Read-only instances support the monitoring and alerting for up to 20 performance metrics such as the disk capacity, IOPS, number of connections, CPU utilization, and network traffic.

Limits

  • The maximum number of read-only instances allowed varies based on the memory capacity.
    Database engine Memory capacity Maximum number of read-only instances
    MySQL ≥ 64 GB 10
    < 64 GB 5
  • You cannot configure backup policies or manually create backups for read-only instances, because these are already configured or created on the primary instance.
  • Take note of the following limits on instance restoration:
    • You cannot create a temporary read-only instance from a data backup file or a specific point in time, nor can you overwrite a read-only instance by using a data backup file.
    • After a read-only instance is created, you cannot use a data backup file to restore it in overwrite mode.
  • You cannot migrate data to read-only instances.
  • You cannot create or delete databases on read-only instances.
  • You cannot create or delete accounts, authorize accounts, or change the passwords of accounts on read-only instances.

Instance creation

For more information, see Create a read-only ApsaraDB RDS for MySQL instance.

FAQ

  • Can I manage accounts created on a primary instance from its read-only instances?

    No, although the accounts created on a primary instance are synchronized to its read-only instances, they cannot be managed on the read-only instances. In addition, the accounts only have read permissions on the read-only instances.

  • Can I pause the fee deduction for read-only instances? And can I set the read weights of read-only instances to 0 to stop the billing?

    No, you cannot pause the fee deduction for read-only instances. However, you can release the read-only instances when you no longer need them. For more information, see Release an RDS MySQL instance.