4.1.4. Design a Disaster Recovery Solution
š” First Principle: A robust disaster recovery (DR) solution, driven by business-defined objectives for recovery time (RTO) and data loss (RPO), is essential for ensuring business continuity in the face of a catastrophic regional outage.
Scenario: You are designing a DR solution for a critical customer-facing application. The business requires an RTO of less than 30 minutes and an RPO of less than 5 minutes in case of a full regional outage. You need to select a suitable DR strategy that balances these stringent requirements with cost.
A robust disaster recovery (DR) solution ensures business continuity by enabling rapid restoration of critical systems and data after a catastrophic event.
Key Design Considerations:
- Recovery Time Objective (RTO): The maximum acceptable duration of downtime after a disaster.
- Recovery Point Objective (RPO): The maximum acceptable amount of data loss measured in time.
- Replication Strategy: Choose between active-active or active-passive replication. Azure Site Recovery (ASR) is key for orchestrating replication.
- Network Design: Plan for IP address retention and DNS updates (e.g., Azure Traffic Manager) to ensure seamless failover.
- Testing and Validation: Regularly test the DR plan through non-disruptive drills (e.g., ASR test failovers).
- Deployment Models:
- Backup and Restore: Highest RTO/RPO, lowest cost.
- Pilot Light: A minimal core infrastructure is kept running in the recovery region.
- Warm Standby: A scaled-down, fully functional production replica is continuously running.
- Multi-Site Active/Active: Application is fully deployed and active in multiple Regions.
ā ļø Common Pitfall: Implementing a DR strategy without regularly testing it. An untested DR plan is likely to fail during a real disaster due to configuration drift, outdated procedures, or unforeseen dependencies.
Key Trade-Offs:
- RTO/RPO vs. Cost: The lower your RTO and RPO (i.e., the faster you need to recover with less data loss), the more expensive and complex your DR strategy will be.
Reflection Question: How does analyzing the required Recovery Time Objective (RTO) and Recovery Point Objective (RPO) fundamentally influence the choice and complexity of your disaster recovery solution (e.g., warm standby vs. active-active), balancing cost with rapid restoration and minimal data loss?