Disaster Recovery Strategy Design — AWS Solutions Architect Pro (SAP-C02)
Pilot Light vs Warm Standby: Hours vs Minutes of RTO
Pilot light keeps only data replicated to the DR region; compute resources are stopped or not provisioned. Recovery requires scaling compute before the environment can serve any traffic, making RTO measured in hours. Warm standby runs a reduced-capacity live environment in the DR region that can serve traffic immediately at reduced throughput, with RTO in tens of minutes. Active-active eliminates recovery time entirely because both regions continuously serve traffic. Backup-and-restore requires a full restore before any compute can start and has the longest RTO of all four patterns. SAP-C02 places the wrong DR tier as a distractor when its RTO characteristic is incompatible with the recovery time stated in the scenario.
What This Pattern Tests
The exam gives RPO and RTO targets and tests which DR tier matches. Backup/Restore stores snapshots in S3 cross-region — RPO = time since last backup, RTO = hours (restore + warm up). Pilot Light runs minimum infrastructure in DR region (database replica, no compute) — RTO = minutes (scale up compute). Warm Standby runs a scaled-down copy of production — RTO = seconds (scale up to full capacity). Multi-Site Active-Active runs full production in both regions — RTO ≈ 0 (Route 53 health check failover). The trap is choosing Multi-Site for RTO of 1 hour (Warm Standby suffices at 1/4 the cost) or Backup/Restore for RTO of 15 minutes (restore takes hours).
Decision Axis
RPO/RTO targets determine DR tier. Cost scales inversely with recovery time. Do not over-buy or under-buy.
Associated Traps
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Decision Rules
Determine whether warm standby (reduced-capacity standby compute with continuous replication and automated DNS failover) satisfies the stated 1-hour RPO and 15-minute RTO at materially lower cost than multi-site active-active, which runs full duplicate production capacity continuously and is unjustified by the recovery objectives.
Domain Coverage
Difficulty Breakdown