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.

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.

The database system is generally an important part of an IT system and has high requirements on storage I/O performance. You can select a storage type based on service demands. You cannot change the storage type after the DB instance is created.

Table 15-6 lists the DB engines and versions supported by RDS.

For new applications, you are advised to use the latest major version of the DB engine, for example, MySQL 5.7. When you create a DB instance, you can select a major DB engine version only (such as MySQL 5.7). The system will automatically select an appropriate minor version (such as 5.7.31) for you. After the DB instance is created, you can view the minor version in the DB Engine Version column on the Instances page. The DB engine and version vary according to site requirements.