Confluence can be connected to an RDS MySQL database. Instruction is generally similar to what's described in the following documentation: Database Setup For MySQL.

During Step 8 (Set up your database connection in the Confluence Setup Wizard), make sure that the JDBC connection follows the following format:

jdbc:mysql://test.us.rds.amazonaws.com:3306/myawsdbname

Similarly, use the format above for datasource connection URL.