Updated on 2023-08-09 GMT+08:00

DB Instance Types

The smallest management unit of RDS is the DB instance. A DB instance is an isolated database environment on the cloud. Each DB instance can contain multiple user-created databases, and you can access a DB instance using the same tools and applications that you use with a stand-alone DB instance. You can easily create or modify DB instances using the management console or HTTPS-compliant application programming interfaces (APIs). RDS does not have limits on the number of running DB instances. Each DB instance has a DB instance identifier.

DB instances are classified into the following types.

Table 1 DB instance types

DB Instance Type




A single-node architecture is more cost-effective than a primary/standby DB pair.

If a fault occurs on a single instance, the instance cannot recover in a timely manner.


An HA architecture. In a primary/standby pair, each instance has the same instance class.

  • When a primary instance is being created, a standby instance is provisioned synchronously to provide data redundancy. The standby instance is invisible to you after being created.
  • If a failover occurs due to a primary instance failure, your database client will be disconnected briefly. You need to reconnect the client to the instance.

Read replica

A single-node architecture (without a standby node)

  • A read replica is a single-node instance. If the physical server hosting a read replica is faulty or database replication between the read replica and its primary instance is abnormal, it takes a long time to rebuild and restore the read replica (depending on the data volume).

You can use RDS to create and manage DB instances running various DB engines.

For details about differences and function comparison between different instance types, see DB Instance Introduction and Function Comparison.