Disaster recovery (DR) planning often feels abstract until disaster strikes. Cloud computing has transformed DR from expensive, complex infrastructure to flexible, scalable services—but the planning and testing remain critical.
Key Concepts
Recovery Time Objective (RTO)
How long can you be down? RTO is the maximum acceptable time between disaster and recovery. An RTO of 4 hours means systems must be restored within 4 hours.
Recovery Point Objective (RPO)
How much data can you lose? RPO is the maximum acceptable data loss measured in time. An RPO of 1 hour means you might lose up to 1 hour of data.
Cost vs. Recovery: Shorter RTO and RPO require more sophisticated (and expensive) solutions. A business decision, not just technical.
| RTO/RPO Target | Typical Solution | Cost |
|---|---|---|
| Days | Backup/Restore | Lowest |
| Hours | Pilot Light / Warm Standby | Moderate |
| Minutes | Hot Standby | High |
| Near-zero | Active-Active Multi-Region | Highest |
DR Strategies
Backup and Restore
Simplest approach: regular backups to a separate region. In disaster, provision infrastructure and restore from backup. Longest RTO (hours to days) but lowest cost.
Pilot Light
Core systems replicated but not running (or running minimally) in DR region. Databases replicated, infrastructure defined in code. In disaster, scale up and start systems. RTO of hours.
Warm Standby
Scaled-down but running environment in DR region. All components active, just smaller. In disaster, scale up to production capacity. RTO of minutes to hours.
Hot Standby (Active-Active)
Full production environment in multiple regions, both serving traffic. In disaster, route traffic away from failed region. Near-zero RTO but highest cost.
Cloud DR Advantages
Why Cloud Simplifies DR
- No upfront investment: Pay for DR infrastructure when you use it
- Geographic distribution: Multiple regions available instantly
- Infrastructure as Code: Rebuild environments quickly from templates
- Managed services: Built-in replication and backup
- Elastic scaling: DR environment can start small, scale when needed
Implementation Considerations
Data Replication
Database replication to DR region. Synchronous for zero data loss (higher latency); asynchronous for better performance (some data loss risk). Choose based on RPO requirements.
DNS and Traffic Management
Route 53, Azure Traffic Manager, or similar for failover routing. Health checks detect failures. DNS changes route traffic to DR. Consider DNS TTL—lower TTL enables faster failover but increases DNS queries.
Application State
Stateless applications are easier to recover. State stored in replicated databases or distributed caches. Session data, user uploads—all need replication strategy.
Dependencies
Map all dependencies. External APIs, SaaS services, on-premise systems. DR plan must account for all dependencies, not just your infrastructure.
Testing and Validation
Untested DR is not DR. Many organisations have DR plans that have never been validated. During actual disaster, they discover the plan doesn't work.
Types of DR Tests
- Tabletop exercise: Walk through the plan on paper. Identify gaps in documentation and process.
- Functional test: Actually perform failover in controlled conditions. Validate technical procedures work.
- Full simulation: Simulate actual disaster scenario. Include non-technical aspects: communication, decision-making.
Test Frequency
At minimum, test annually. Quarterly is better. Major infrastructure changes should trigger additional testing. Document results and improve the plan.
DR Runbook
Document the exact steps to execute DR:
- Detection: How do we know there's a disaster?
- Decision: Who declares disaster? What's the threshold?
- Communication: Who needs to know? How do we reach them?
- Execution: Step-by-step technical procedures
- Validation: How do we confirm recovery is successful?
- Return: Process to fail back to primary when resolved
Summary
Cloud enables DR strategies that were previously only available to large enterprises. Choose your strategy based on business requirements (RTO/RPO) and budget. Remember that shorter recovery targets cost more.
Whatever strategy you choose, test it. Document procedures in runbooks. Review and update as your environment changes. Disaster recovery isn't a one-time project—it's an ongoing discipline.