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

Overview

While a read-only instance is being created, the data is replicated from the secondary instance. The data on the secondary instance is consistent with that on the primary instance. After an update to the data on the primary instance is complete, this update is immediately synchronized to all of the read-only instances.

Note
  • The primary instance must belong to the dedicated instance family and provide at least 8 CPU cores and 32 GB of memory.
  • Each read-only instance works in a single-node architecture, where no instances are provided as backups.
The following figure shows the topology of read-only instances in a database system.PPAS topology

Billing

You are charged an hourly rate for each read-only instance based on pay-as-you-go billing.

Features

  • Billing method: Read-only instances use pay-as-you-go billing to reduce costs.
  • Region and zone: Read-only instances reside in the same region as the primary instance, but possibly in different zones.
  • Specifications and storage capacity: The specifications and storage capacity of read-only instances cannot be lower than those of the primary instance.
  • Change the network type of an RDS PPAS instance: The network type of read-only instances can be different from that of the primary instance.
  • Account and database management: Read-only instances do not require database or account maintenance, because their database and account information is synchronized with the primary instance.
  • IP address whitelist: While read-only instances are being created, they automatically replicate the IP address whitelists of the primary instance. However, the IP address whitelists on read-only instances are independent of the IP address whitelists that are configured on the primary instance. For more information about how to modify the whitelists of a read-only instance, see Configure a whitelist for an ApsaraDB RDS for PPAS instance.
  • Monitoring and alerting: You can monitor system performance metrics, such as the disk usage, input/output operations per second (IOPS), maximum number of connections, and CPU utilization.

Limits

  • A maximum of five read-only instances are allowed for a primary instance.
  • Read-only instances do not support backup settings or manual backups.
  • 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.

FAQ

Can I manage accounts created in the primary instance from its read-only instances?

No, although accounts created on the primary instance are replicated to its read-only instances, you cannot manage the accounts on the read-only instances. Read-only instances only allow accounts to read data.