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3.1.1.1. Multi-AZ and Multi-Region Deployments (Compute, Data Layer)
3.1.1.1. Multi-AZ and Multi-Region Deployments (Compute, Data Layer)
Multi-AZ protects against single datacenter failures. Multi-Region protects against entire region outages and reduces latency for global users. The exam expects you to know which services support each pattern and the trade-offs involved.
Compute layer HA patterns:
| Pattern | Mechanism | Failover Time |
|---|---|---|
| EC2 + ASG across AZs | ASG replaces failed instances in healthy AZs | Minutes |
| ECS/EKS across AZs | Scheduler places tasks in available AZs | Seconds |
| Lambda | Automatically multi-AZ within a region | Seamless |
| EC2 Multi-Region | Separate ASGs per region + Route 53 failover | Minutes |
Data layer HA patterns:
| Service | Multi-AZ | Multi-Region |
|---|---|---|
| RDS | Synchronous standby, automatic failover (1-2 min) | Read replicas, manual promotion |
| Aurora | Up to 15 read replicas across AZs, auto failover (30s) | Global Database, <1s replication lag |
| DynamoDB | Automatic across 3 AZs | Global Tables (active-active, seconds lag) |
| ElastiCache Redis | Multi-AZ with auto-failover | Global Datastore (cross-region read replicas) |
| S3 | Automatic across ≥3 AZs | Cross-Region Replication (CRR) |
Exam Trap: RDS Multi-AZ is not a read scaling solution — the standby is for failover only and cannot serve read traffic. For read scaling, use read replicas. Aurora is different: its read replicas do serve read traffic AND participate in failover. If the exam asks about both read scaling and HA, Aurora read replicas are the answer.
Written byAlvin Varughese•Founder•15 professional certifications