An Amazon Relational Database Service (Amazon RDS) DB instance is an isolated database environment running in the cloud. The DB Instance Master Username is the username used to connect to the DB instance and perform administrative tasks or access the data stored within that instance. It was detected that RDS database instance {AwsRdsDbInstance} is using a default master username - '{AwsRdsDbInstance.MasterUsername}'. Default administrative usernames on Amazon RDS databases are public knowledge. When creating an Amazon RDS database, you should change the default administrative username to a unique value to reduce the risk of unintended access.