2.2.2.2. Disaster Recovery (DR) Strategies: RPO, RTO

💡 First Principle: Disaster Recovery (DR) strategies rapidly restore critical systems and data after disruptive events, minimizing downtime and data loss for continuous business operations.

Disaster Recovery (DR) strategies rapidly restore critical systems and data after disruptive events, minimizing downtime and data loss for continuous business operations.

Disaster Recovery (DR) is a comprehensive plan to prepare for and recover from major outages or disasters that could affect an entire data center or AWS Region. Two fundamental metrics guide DR strategy:

• Recovery Time Objective (RTO): The maximum tolerable duration of time that a system or application can be down after a disaster. It defines how quickly you need to recover (e.g., 15 minutes, 4 hours). A low RTO demands rapid recovery mechanisms.
• Recovery Point Objective (RPO): The maximum tolerable amount of data loss, measured in time. It defines how much data you can afford to lose (e.g., 0 seconds, 5 minutes, 1 hour). A low RPO requires frequent backups or continuous replication.

Key DR Strategies (from highest RTO/RPO/lowest cost to lowest RTO/RPO/highest cost):

1. Backup and Restore: Longest RTO/RPO, lowest cost.
2. Pilot Light: Key components always running, minimal infrastructure.
3. Warm Standby: Scaled-down, fully functional replica, continuously updated.
4. Multi-Site Active/Active: Fully deployed in multiple Regions, serving traffic simultaneously, near-zero RTO/RPO.

Scenario: An organization implements a pilot light DR strategy for its e-commerce platform on AWS, targeting an RPO of 15 minutes (S3 backup) and an RTO of 4 hours (launching EC2 from AMIs).

Visual: Disaster Recovery (DR) Strategies (RPO/RTO vs. Cost)

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⚠️ Common Pitfall: Choosing a DR strategy that is too expensive or complex for the actual RPO/RTO requirements of the workload. Not all applications need active-active multi-region DR.

Key Trade-Offs:

• RPO/RTO vs. Cost: There's a direct correlation: lower RPO/RTO (less data loss, faster recovery) typically means higher cost due to increased infrastructure and replication.

Reflection Question: How do RPO and RTO influence the choice and cost of a DR strategy for different business functions, balancing acceptable downtime/data loss with financial investment?