Amazon Relational Database Service ( Amazon RDS )

Correct Answer: 2

When you create a read replica, you first specify an existing DB instance as the source. Then Amazon RDS takes a snapshot of the source instance and creates a read-only instance from the snapshot. Amazon RDS then uses the asynchronous replication method for the DB engine to update the read replica whenever there is a change to the primary DB instance. The read replica operates as a DB instance that allows only read-only connections. Applications connect to a read replica the same way they do to any DB instance. Amazon RDS replicates all databases in the source DB instance.

When creating a read replica, there are a few things to consider. First, you must enable automatic backups on the source DB instance by setting the backup retention period to a value other than 0. This requirement also applies to a read replica that is the source DB instance for another read replica. For MySQL DB instances, automatic backups are supported only for read replicas running MySQL 5.6 and later, but not for MySQL versions 5.5. To enable automatic backups on an Amazon RDS MySQL version 5.6 and later read replica, first create the read replica, then modify the read replica to enable automatic backups.

Hence, the correct answer is: The backup retention period of the RDS DB instance is 0.

The option that says: The proper AWS CLI command to create a read replica for RDS is CreateDBInstance is incorrect. This choice is correct if used to create an instance for an Amazon Aurora DB Cluster (applicable to Aurora read replicas).

The option that says: The source DB instance used in the create-db-instance-read-replica command is another read replica is incorrect as explained above.

The option that says: The source DB instance has to be converted to Single-AZ first to create a read replica from it is incorrect. You can create a read replica from either single-AZ or Multi-AZ DB instance deployments.

References:
https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_ReadRepl.html
https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_MySQL.Replication.ReadReplicas.html

Note: This question was extracted from our AWS Certified Database Specialty Practice Exams.