🃏 Resilience & DR Flashcards

Q: What are the 4 DR strategies in order of RTO?

A: Backup & Restore (hours) → Pilot Light (10s min) → Warm Standby (minutes) → Active-Active (real-time). Cost increases with lower RTO.

Q: What is pilot light DR?

A: Core infrastructure (DB replicas) running in DR region but compute is off. Scale up compute when failover needed. RTO: 10s of minutes.

Q: What is warm standby DR?

A: Scaled-down but fully functional copy in DR region. Scale to full production capacity during failover. RTO: minutes.

Q: How does Route 53 health check failover work?

A: Health checks monitor endpoints. Failover routing policy routes traffic to secondary when primary is unhealthy. Can be alias or non-alias records.

Q: What is ECS circuit breaker?

A: Monitors task health during deployments. If tasks keep failing (reach threshold), automatically rolls back to the last stable deployment without manual intervention.

Q: What is Auto Scaling Group health check grace period?

A: Time after launch before health checks start. Prevents premature termination while application initializes. Set based on app startup time.

Q: How does DynamoDB Global Tables work for DR?

A: Active-active multi-region replication. All regions accept writes with last-writer-wins conflict resolution. Sub-second replication latency.

Q: What is S3 Cross-Region Replication?

A: Automatic async replication of objects to a bucket in another region. Requires versioning. Can replicate entire bucket or filter by prefix/tag.

Q: What is a well-architected operational readiness review?

A: Validates that operational procedures, runbooks, monitoring, and team readiness are in place before launching or during operations.

Q: How do you test DR plans without impacting production?

A: Use AWS Fault Injection Simulator (FIS) for controlled experiments. Test runbooks, failover procedures, and recovery automation safely.