Multi-Az And Data Durability Design — AWS Solutions Architect (SAA-C03)
High availability and data durability are not equivalent
"Multi-AZ" means failover availability — the database stays accessible if one AZ fails. It does not protect against data deletion, corruption, or application-layer errors. S3's eleven-nines durability refers to object persistence, not availability. Candidates treat Multi-AZ as a complete data protection strategy. The exam tests whether you recognize that automated backups, point-in-time recovery, and cross-region replication address data-loss scenarios that Multi-AZ cannot. When the scenario involves data recovery rather than uptime, the correct answer changes.
What This Pattern Tests
The exam tests AZ-level resilience as the baseline design pattern. RDS Multi-AZ deploys a synchronous standby in another AZ — automatic failover in 60-120 seconds, no data loss. Read Replicas use asynchronous replication — no automatic failover, potential data lag. EBS volumes are AZ-scoped — an AZ failure loses access to the volume. S3 stores objects across at least 3 AZs automatically. The trap is confusing Multi-AZ (high availability, synchronous) with Read Replicas (read scaling, asynchronous) or assuming EBS survives an AZ failure (it does not without snapshots).
Decision Axis
Availability target determines AZ design: 99.9% may need single-AZ with backups, 99.99% needs Multi-AZ, 99.999% needs Multi-Region.
Associated Traps
More Top Traps on This Exam
Decision Rules
Whether synchronous replication with automatic standby promotion (RDS Multi-AZ) or asynchronous replication with manual promotion (RDS Read Replica) satisfies a stated RPO under one minute with no manual failover intervention.
Domain Coverage
Difficulty Breakdown