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Updated on 2026-04-24 GMT+08:00
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DB Instance Types

The smallest management unit of RDS is 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 unique identifier.

DB instances are classified into the following types.

Table 1 DB instance types

DB Instance Type

Description

Notes

Single-node

A single-node architecture is used. It is more cost-effective than mainstream primary/standby DB instances.

If a fault occurs on a single-node instance, the instance cannot recover in a timely manner. Do not use single-node instances in any production environment.

Primary/Standby

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

The primary and standby instances can be deployed in different AZs.
  • 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 primary instance fails, a failover is triggered. Database clients experience a brief interruption during this process and must be able to reconnect.
  • The default replication mode between the primary and standby instances is as follows:
    • RDS for MySQL: semi-synchronous
    • RDS for PostgreSQL: asynchronous
    • RDS for SQL Server uses asynchronous replication between the primary instance and read replicas.

Read replica

A single-node architecture (without a standby node)
  • Read replicas help reduce read pressure on single-node or primary/standby instances, but they cannot be purchased separately. For a single-node read replica, if the physical server hosting it fails or if replication with its primary instance is abnormal, you need to rebuild and restore the read replica. The recovery time will vary depending on the data volume.
  • Database proxy is recommended for read-intensive workloads. Before using database proxy, ensure that you have purchased more than one read replica. If a single read replica is faulty, database proxy can distribute traffic to other read replicas.

Cluster

The Microsoft Always On architecture. There is one primary node, one standby node, and up to five read-only nodes. It features higher availability, reliability, and scalability.

Only for RDS for SQL Server.

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

For details about differences and function comparison between different MySQL instance types, see RDS for MySQL Product Series.

For details about differences and function comparison between different PostgreSQL instance types, see RDS for PostgreSQL Product Series.

For details about differences and function comparison between different SQL Server instance types, see RDS for SQL Server Product Series.

Parent topic: DB Instance Description