Master the difference between Multi-AZ and Read Replicas, understand Aurora's advantages, and know when to use RDS versus DynamoDB.
RDS — Managed Relational Databases
RDS is a managed database service. AWS handles the undifferentiated heavy lifting: hardware provisioning, OS patching, database software updates, automated backups, and Multi-AZ failover. You focus on your data.
Teacher Note: Without RDS, a DBA spends 30-40% of their time on maintenance tasks: patching OS, upgrading database software, configuring backups, setting up replication. RDS handles ALL of this automatically so your team focuses on business logic.
Supported Database Engines
| Engine | Best For |
|---|
| MySQL | Web applications, WordPress, PHP apps |
| PostgreSQL | Complex queries, GIS, advanced data types |
| MariaDB | MySQL-compatible, community-driven |
| Oracle | Enterprise applications, legacy systems |
| SQL Server | Microsoft stack, .NET applications |
| Aurora | AWS-native — 5x MySQL, 3x PostgreSQL performance |
Multi-AZ vs Read Replicas — Know the Difference!
| Feature | Multi-AZ | Read Replicas |
|---|
| Purpose | HIGH AVAILABILITY — automatic failover | READ SCALABILITY — offload read traffic |
| Replication | SYNCHRONOUS (zero data loss) | ASYNCHRONOUS (small lag possible) |
| Standby readable? | NO — standby is passive, not readable | YES — each replica has its own endpoint |
| Failover | Automatic, same endpoint, 60-120 seconds | Manual promotion required |
| Max replicas | 1 standby (Multi-AZ standard) or 2 (Multi-AZ cluster) | Up to 5 (15 for Aurora) |
| Cross-region | No (same region only) | Yes — cross-region read replicas possible |
RDS Aurora — The Best of Both Worlds
- Shared distributed storage across 6 copies in 3 AZs — survives 2 AZ failures
- Auto-grows from 10GB to 128TB — no storage planning needed
- 15 read replicas with under 10ms lag
- Aurora Serverless v2: auto-scales compute in 0.5 ACU increments within seconds
- Aurora Global Database: replicates across 5 regions with under 1 second lag
Exam Tip: The MOST common exam trap: Multi-AZ is for AVAILABILITY (failover), NOT performance. Read Replicas are for PERFORMANCE (scaling reads). If the question says high availability or disaster recovery — think Multi-AZ. If it says too many read requests — think Read Replicas.