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Disaster Recovery (DR)

Disaster recovery is the plan and infrastructure for restoring service after catastrophic failure (region outage, data center loss, ransomware). Defined by RPO (how much data loss is acceptable) and RTO (how quickly service must resume). DR requires cross-region replication, tested runbooks, and regular drills.

Definition

Disaster recovery addresses failures beyond what HA handles – entire region outages, natural disasters, or data corruption that replication propagates. DR is defined by two metrics: RPO (Recovery Point Objective – maximum acceptable data loss, measured in time) and RTO (Recovery Time Objective – maximum acceptable downtime). A system with RPO=1h and RTO=4h can lose up to 1 hour of data and must be operational within 4 hours of disaster declaration. DR tiers: backup/restore (RPO hours-days, RTO hours-days, lowest cost), pilot light (critical systems replicated, scale up on activation, RPO minutes, RTO minutes-hours), warm standby (scaled-down replica running in DR region, RPO seconds-minutes, RTO minutes), and multi-site active-active (both regions serve traffic, RPO=0, RTO=0, highest cost). The most common DR failure: untested runbooks. Organizations discover during an actual disaster that their backup restore takes 3x longer than expected, replicas are weeks behind, or key credentials are stored only in the failed region.

Examples

  • –AWS: S3 cross-region replication + RDS cross-region read replica + Route 53 failover
  • –RPO=0: synchronous multi-region writes (expensive, adds latency to every write)
  • –DR drill: quarterly simulate region failure, measure actual RTO, document gaps

Related Protocols

tcp

Related Terms

Failover

Failover is the automatic transfer of traffic from a failed primary system to a standby replica. Database failover promotes a replica to primary. DNS failover routes to a backup IP. Load balancer failover removes failed backends. Recovery time (RTO) depends on detection speed and promotion mechanism – seconds for load balancer, minutes for database.

High Availability (HA)

High availability is a system design that minimizes downtime by eliminating single points of failure. Measured in 'nines' – 99.9% (8.7h downtime/year), 99.99% (52min/year), 99.999% (5min/year). Requires: redundant components, automatic failover, health monitoring, and tested recovery procedures.

RPO and RTO

RPO (Recovery Point Objective) is the maximum acceptable data loss measured in time – how far back you can roll back. RTO (Recovery Time Objective) is the maximum acceptable downtime – how quickly you must be back online. RPO=0 means zero data loss (synchronous replication). RTO=0 means zero downtime (active-active). Both cost exponentially more as they approach zero.