Building a disaster recovery (DR) solution: Design considerations
Design considerations
When designing a Disaster Recovery (DR) solution, several factors need to be considered to ensure that the system is resilient, cost-effective, and aligned with your organization’s recovery objectives. Here’s a comprehensive list:
1. Business Requirements
Recovery Time Objective (RTO):
- How quickly should the system be restored after a disaster?
- Example: 1 hour, 4 hours, or 24 hours.
Recovery Point Objective (RPO):
- How much data loss is acceptable in the event of a disaster?
- Example: 0 data loss (requires synchronous replication) vs. a few minutes (asynchronous replication).
Criticality of Workloads:
- Identify mission-critical workloads versus those that can tolerate downtime.
2. Types of Failures to Mitigate
Application-Level Failures:
- Ensure redundancy in application components like load balancers, application servers, and database connections.
Infrastructure-Level Failures:
- Address issues like hardware failures, network outages, or storage issues.
Region-Level Failures:
- Plan for scenarios like a full-region outage (e.g., AWS Mumbai region going offline).
Cloud Provider-Level Failures:
- Rare but catastrophic, such as a cloud provider outage or breach. Consider multi-cloud setups.
3. DR Solution Architecture
Replication Strategy:
- Synchronous vs. Asynchronous replication.
- Multi-region, multi-zone, or multi-cloud setups.
Active-Active or Active-Passive Setup:
- Active-Active: Both regions handle traffic simultaneously.
- Active-Passive: One region handles traffic, while the other remains on standby.
Data Consistency Models:
- Strong consistency, eventual consistency, or custom consistency requirements based on the workload.
4. Database-Specific Considerations
Replication Latency:
- How quickly data is replicated across nodes or regions.
- Example: MongoDB Atlas vs. Amazon RDS replication latency.
Quorum Configurations:
- How many nodes must be available for the system to remain operational?
Pre-Warming:
- For systems like MongoDB or RDS, how long does it take to prepare new nodes during failover?
5. Network Design
Latency:
- Placement of nodes in geographically distributed regions.
- Minimize latency while ensuring fault tolerance.
Bandwidth Costs:
- Cross-region replication or communication costs.
6. Testing and Training
Strategy
- How will you ensure your DR applications are ready to serve traffic all the time?
DR Playbook:
- Document detailed steps for failover, recovery, and fallback.
Training:
- Train teams to respond to DR scenarios effectively.
7. Cost and Resource Optimization
Budget Constraints:
- Evaluate the costs of maintaining redundant resources (e.g., compute, storage, network).
Trade-offs:
- The balance between high availability and cost.
- Example: Use smaller instance types for passive nodes to reduce costs in an active-passive setup.
By addressing these seven considerations, you can design a robust DR solution that aligns with your operational, technical, and business needs.