A. Configure both of the Aurora Replicas to the same instance class as the primary DB instance. Enable cache coherence on the DB cluster, set the primary DB instance failover priority to tier-0, and assign a failover priority of tier-1 to the replicas.
B. Deploy an AWS Lambda function that calls the DescribeDBInstances action to establish which instance has failed, and then use the PromoteReadReplica operation to promote one Aurora Replica to be the primary DB instance. Configure an Amazon RDS event subscription to send a notification to an Amazon SNS topic to which the Lambda function is subscribed.
C. Configure one Aurora Replica to have the same instance class as the primary DB instance. Implement Aurora PostgreSQL DB cluster cache management. Set the failover priority to tier-0 for the primary DB instance and one replica with the same instance class. Set the failover priority to tier-1 for the other replicas.
D. Configure both Aurora Replicas to have the same instance class as the primary DB instance. Implement Aurora PostgreSQL DB cluster cache management. Set the failover priority to tier-0 for the primary DB instance and to tier-1 for the replicas.