design-multi-region-architecture

Design Multi-Region Architecture

Design cloud systems that remain available and performant across geographic failures.

Why This Is Best Practice

Adopted by: Netflix, Amazon, Google, Stripe, financial institutions under DORA/BCBS239 regulation Impact: Achieve 99.99%+ availability; reduce latency by 40-60% for globally distributed users; meet RTO < 15 min targets Why best: Single-region deployments create single points of failure; multi-region distributes blast radius and puts compute near users

Sources: AWS Well-Architected Reliability Pillar (2023); Google Cloud Architecture Framework; NIST SP 800-34 Rev.1

Steps

1. Define availability targets — Set RTO/RPO per service tier (tier 1: RTO < 15 min, RPO < 1 min; tier 2: RTO < 4 hr, RPO < 1 hr). These drive region count and replication strategy.

2. Select regions — Choose primary, secondary, and optional tertiary regions based on: user latency (<100 ms rule), data residency law (GDPR, PDPA), cloud provider availability, and inter-region latency (prefer <50 ms pairs).

3. Choose a multi-region pattern — Active-active: traffic served from all regions simultaneously (highest complexity, lowest RTO). Active-passive: standby region takes over on failure (simpler, higher RTO). Pilot-light: minimal standby scaled on failover.

4. Design data replication — Synchronous replication for zero RPO (adds latency); asynchronous for low-latency writes with non-zero RPO. Use CRDTs or last-write-wins for conflict resolution. Partition databases by geography where data residency requires it.

5. Implement global load balancing — Route traffic via anycast DNS (Route 53, Cloud DNS) or global load balancers with health checks. Use latency-based or geolocation routing. Set failover thresholds and TTLs (<30 s).

6. Handle consistency trade-offs — Apply CAP theorem: during partition, choose availability or consistency per service. Use eventual consistency for non-critical data; strong consistency only where required (financial transactions).

7. Design stateless compute — Ensure application servers carry no local state. Externalize sessions to distributed caches (Redis Cluster, Memorystore). Store ephemeral files in object storage, not local disk.

8. Implement observability per region — Deploy independent monitoring stacks per region. Aggregate metrics globally but alert regionally. Measure inter-region replication lag as a key metric.

9. Test failover regularly — Run game days quarterly; automate chaos experiments (inject region failure in staging). Measure actual RTO vs target; update runbooks.

10. Document runbooks — Write step-by-step regional failover procedures. Assign ownership. Test runbooks annually and after every architecture change.

Rules

• Never share a single database across regions without replication — it becomes your single point of failure.
• Always test failover before you need it; untested failover plans fail when it counts.
• Match region count to RTO/RPO requirements, not aspirations — each additional region multiplies operational complexity.
• Treat inter-region bandwidth costs as a first-class architectural concern.

Common Mistakes

• Assuming active-active is always better — it requires conflict resolution logic; active-passive is often sufficient and far simpler.
• Ignoring replication lag — asynchronous replication means data loss on failover; measure and communicate RPO honestly.
• Forgetting third-party dependencies — DNS providers, CDNs, and SaaS tools may be single-region; audit all external dependencies.
• Underestimating data residency complexity — GDPR and similar laws may prohibit cross-border replication; consult legal before designing replication topology.

When NOT to Use

• Internal tools or low-criticality workloads where downtime cost is less than multi-region overhead
• Early-stage products where simplicity and iteration speed outweigh availability guarantees
• Applications with regulatory requirements that prohibit data leaving a single jurisdiction