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 create and modify DB instances using the management console or 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	Description
Single	Uses a single-node architecture. More cost-effective than primary/standby DB instances.
Primary/Standby	Uses an HA architecture with one master node and one slave node. The instance classes of the nodes are the same.
Read replica	Uses a single-node architecture (without a standby node).
Cluster	Uses the Microsoft Always On architecture with one master node, one slave node, and up to five read-only nodes. It features higher availability, reliability, and scalability.