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Amazon RDS & Aurora — Relational
Managed relational databases. Multi-AZ for availability, read replicas for scale.
What it is
Managed relational databases (RDS engines; Aurora is the cloud-native, higher-performance option).
The distinction that trips everyone
- Multi-AZ = synchronous standby, automatic failover => availability (not scaling).
- Read Replicas = asynchronous copies serving reads => read scaling (not automatic failover).
Key architectural decisions
- Need HA? Multi-AZ. Read-heavy? Add read replicas. Both? Do both.
- Aurora stores six copies across three AZs, fails over fast, and offers Serverless v2 for variable load.
- Offload hot reads further with ElastiCache.
Gotchas & exam traps
- "Automatic failover with minimal downtime" => Multi-AZ. "Offload read traffic" => Read Replicas.
- Cross-Region read replicas support DR and low-latency global reads.
- Relational + complex joins/transactions => RDS/Aurora; simple key-value at scale => DynamoDB.
The architect view
Most "which database" questions are answered by access pattern. Reach for RDS/Aurora when you truly need relational semantics, and use Multi-AZ vs replicas deliberately — they solve different problems.