This topic provides an overview of read-only ApsaraDB RDS for MySQL instances. If your database system receives a small number of write requests but a large number of read requests, a single primary RDS instance may be overwhelmed by the read requests and your workloads may be interrupted. To offload read requests from the primary RDS instance, you can create one or more read-only RDS instances. Read-only RDS instances help increase the read capability of your database system and the throughput of your application.

For information about read-only RDS instances that run different database engines, see the following topics:

Background information

When a read-only RDS instance is being created, ApsaraDB RDS replicates data from the secondary RDS instance to the read-only RDS instance. Each read-only RDS instance has the same data as the primary RDS instance. After the data on the primary RDS instance is updated, ApsaraDB RDS immediately replicates the data updates to all the read-only RDS instances. You can specify a replication latency on each read-only RDS instance. For more information, see Set a replication delay for a read-only ApsaraDB RDS for MySQL instance.

Note Each read-only RDS instance runs in the high availability architecture that allows the read-only RDS instance to have a secondary instance as a standby.

Prerequisites

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

  • MySQL 8.0 on RDS High-availability Edition or Enterprise Edition
  • MySQL 5.7 on RDS High-availability Edition or Enterprise Edition
  • MySQL 5.6
Note If the primary RDS instance runs MySQL 5.7 on RDS Enterprise Edition, you cannot create read-only RDS instances.In this case, if you require read-only RDS instances, you must submit a ticket.

Billing

Read-only RDS instances support both the pay-as-you-go billing method and the subscription billing method. For more information about the prices of read-only RDS instances, see Read-only ApsaraDB RDS instance types.

Precautions

  • If the primary RDS instance is charged based on the subscription billing method and you want to create a subscription read-only RDS instance, you can configure the read-only RDS instance to have the same subscription period as the primary instance.
  • If the primary RDS instance is locked after it expires, you can still access the read-only RDS instances of the primary RDS instance. However, the statuses of the read-only RDS instances change to Running (Primary Instance Locked).
  • After the primary RDS instance is released, the subscription read-only RDS instances of the primary RDS instance are automatically refunded and released, and the pay-as-you-go read-only RDS instances of the primary RDS instance are directly released.

Usage notes

  • Read-only RDS instances support both the pay-as-you-go billing method and the subscription billing method. The pay-as-you-go billing method is flexible and allows you to release your read-only RDS instances when you no longer need the instances. The subscription billing method is cost-effective for long-term commitments.
  • Read-only RDS instances reside in the same region as the primary RDS instance, but possibly in different zones.
  • The specifications of read-only RDS instances can differ from the specifications of the primary RDS instance. You can change the specifications of read-only RDS instances at any time. We recommend that the specifications of read-only RDS instances be higher than or equal to the specifications of the primary RDS instance. If the specifications of a read-only RDS instance are lower than the specifications of the primary RDS instance, the read-only RDS instance may encounter issues such as high latency or heavy load.
  • The network types of read-only RDS instances can differ from the network type of the primary RDS instance. For more information, see Change the network type of an ApsaraDB RDS for MySQL instance.
  • The databases and accounts on read-only RDS instances are synchronized from the primary RDS instance. Therefore, you do not need to manage databases or accounts on read-only RDS instances.
  • When you create a read-only RDS instance, ApsaraDB RDS replicates the IP address whitelists of the primary RDS instance to the read-only RDS instance. However, the IP address whitelists of the read-only RDS instance are independent of the IP address whitelists that are configured on the primary RDS instance. For more information about how to modify the IP address whitelists of a read-only RDS instance, see Configure an IP address whitelist for an ApsaraDB RDS for MySQL instance.
  • Read-only RDS instances support monitoring and alerting. You can monitor near 20 metrics, such as the disk usage, input/output operations per second (IOPS), number of connections, CPU utilization, and network traffic.

Limits

  • The maximum number of read-only RDS instances that can be created varies based on the memory capacity.
    Database engine Memory capacity Maximum number of read-only RDS instances
    MySQL ≥ 64 GB 10
    < 64 GB 5
  • You cannot configure backup policies or manually create backups for read-only RDS instances. These operations are performed on the primary RDS instance.
  • The following limits are imposed on the data restoration of read-only RDS instances:
    • You cannot create a temporary RDS instance that is used to restore the data of a read-only RDS instance from a data backup file or to a specific point in time. In addition, you cannot overwrite the data of a read-only RDS instance by using a data backup file.
    • After a read-only RDS instance is created, you cannot overwrite the data of the primary RDS instance by using a data backup file.
  • You cannot migrate data to read-only RDS instances.
  • You cannot create or delete databases on read-only RDS instances.
  • You cannot create or delete accounts, authorize accounts, or change the passwords of accounts on read-only RDS instances.

Create a read-only RDS instance

Create a read-only ApsaraDB RDS for MySQL instance

FAQ

  • After I create accounts on my primary RDS instance, can I manage the accounts on the read-only RDS instances?

    No, although the accounts created on your primary RDS instance are synchronized to the read-only RDS instances, you cannot manage the accounts on the read-only RDS instances. The accounts have only the read permissions on the read-only RDS instances.

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

    No, you cannot pause the billing for your read-only RDS instances. If you no longer need your read-only RDS instances, we recommend that you immediately release the instances. For more information, see Release or unsubscribe from an ApsaraDB RDS for MySQL instance.