RTO / RPO / HA Concepts

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Resilience & Disaster Recovery

Design for failure — Auto Scaling, load balancing, and DR strategies keep applications running when instances, AZs, or entire regions go down.

~49 min total7 modules8 quiz questionsDOP-C02 High priority

Resilience on AWS is built around a hierarchy of concepts: individual resource fault tolerance, AZ-level high availability, and region-level disaster recovery. The exam tests whether you know which tool solves which problem, and the trade-offs between cost and RTO/RPO targets.

Core Concepts — Click Each

The Resilience Hierarchy

Region-Level

Disaster Recovery (DR)

Multi-region: Route 53 failover, read replicas, S3 cross-region replication

AZ-Level

High Availability (Multi-AZ)

Multi-AZ: ASG across AZs, RDS Multi-AZ, ALB targets in multiple AZs

Instance-Level

Auto Recovery / ASG Replace

EC2 auto-recovery (CloudWatch alarm), ASG health checks + replacement

Component-Level

Fault Tolerance

S3, DynamoDB, SQS — managed services with built-in FT

🎯Multi-AZ = HA (AZ failure protection). Multi-Region = DR (region failure protection). These are different levels of resilience at different costs. An RDS Multi-AZ instance is not DR — it protects against AZ failure but not region failure.

Availability Math

99%(2 nines)max 3.65 days/year downtime

99.9%(3 nines)max 8.7 hours/year downtime

99.99%(4 nines)max 52 minutes/year downtime

99.999%(5 nines)max 5.25 minutes/year downtime