AWS Certified Solutions Architect Professional SAP-C02 Practice Question

Amazon RDS Multi-AZ deployments that use two readable standbys (also called a Multi-AZ DB cluster) place one writer and two reader/standby DB instances in three different AZs. The cluster uses semisynchronous replication that must be acknowledged by at least one standby, so failovers typically complete in under 35 seconds with zero data loss. The two standbys can take read-only traffic at all times, and the cluster offers a built-in writer (cluster) endpoint as well as a dedicated reader endpoint that load-balances sessions. Because the deployment keeps the engine on RDS for MySQL and stores the redo log on local NVMe storage, transaction-commit latency can be up to twice as fast as the traditional Multi-AZ configuration that relies on shared network storage.

• A Multi-AZ DB instance with one standby fails over in about 60-120 seconds and its standby cannot serve reads, so it misses both the RTO and read-scaling goals.
• An Aurora MySQL cluster would satisfy the timing goals but would change the engine family (contrary to the stated requirement) and introduces different operational characteristics.
• A Single-AZ RDS instance with read replicas plus Route 53 health checks lacks automatic, lossless failover within 35 seconds and still has higher write latency.

Therefore, the Multi-AZ DB cluster with two readable standbys is the only option that satisfies every requirement.