This topic introduces RDS for PostgreSQL read-only instances. For services that involve a small number of write requests but a large number of read requests, a single RDS instance may not be able to resist the read pressure. As a result, services may be affected. To scale the read ability elastically and share data pressure, you can create one or more read-only instances for your RDS instance. The read-only instances can handle massive read requests and increase the application throughput.

Overview

A read-only instance is a read-only copy of the master instance. Changes to the master instance are automatically synchronized to all relevant read-only instances.

Note
  • Read-only instances must be PostgreSQL 10.0 High-Availability instances (with local SSDs).
  • The configuration of the master instance must be at least 8-core 32 GB (dedicated or dedicated-host instance).
  • Each read-only instance adopts a single-node architecture (without slave instances).
The following figure shows the topology of read-only instances.pgsql拓扑图

Pricing

Read-only instances use the Pay-As-You-Go billing method. They are charged once every hour.

Features

Read-only instances offer the following features:

  • Billing method: Pay-As-You-Go. This method is more flexible and cost-effective.
  • Region and zone: A read-only instance must be in the same region as the master instance, but can be in a different zone from the master instance.
  • Specifications and storage capacity: The specifications and storage capacity of a read-only instance cannot be lower than those of the master instance.
  • Network type: The network type of a read-only instance can be different from that of the master instance.
  • Account and database management: Users manage accounts and databases through the master instance rather than read-only instances.
  • Whitelist: When a read-only instance is created, it automatically copies the whitelists of the master instance, but the whitelists of the read-only instance are independent of those of the master instance. You can modify the whitelists of a read-only instance according to Configure a whitelist for an RDS for PostgreSQL instance.
  • Monitoring and alarming: You can monitor system performance metrics, including the disk capacity, IOPS, number of connections, and CPU usage.

Limits

  • Each master instance can have up to five read-only instances.
  • 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 for read-only instances.
  • You cannot create or delete accounts for read-only instances. Additionally, you cannot authorize accounts or change account passwords for read-only instances.

FAQ

Does an account created in the master instance have permissions on read-only instances?

The accounts created in the master instance are automatically synchronized to read-only instances. However, you cannot manage the accounts in the read-only instances. The accounts only have the read permissions for the read-only instances.