Never Down: Multi-Region, Anycast DNS & Failover for Always-On Sites
Written by on Thursday, September 18th, 2025
High-Availability Web Architecture: Multi-Region Hosting, Anycast DNS, Failover and Disaster Recovery for Always-On Sites
Minutes of downtime can cost revenue, trust, and search ranking. Designing for high availability means treating failure as inevitable and building layers of resilience. This overview explains how multi-region hosting, Anycast DNS, and disciplined failover and disaster recovery (DR) combine to keep sites online—even during regional outages or surging traffic.
Multi-Region Hosting
Running your application in multiple regions spreads risk across independent fault domains and brings content closer to users. Two common patterns are:
- Active-active: Traffic is served concurrently from multiple regions. Benefits include low latency and instant failover, but you must solve data consistency and state management.
- Active-passive: One region serves all traffic; another stands by for failover. Simpler for stateful systems but slower recovery and potential cold-start costs.
Example: A media publisher deploys stateless web tiers to us-east-1 and eu-west-1 behind a global load balancer, with shared caches and replicated object storage to serve regional audiences efficiently.
Anycast DNS and Global Traffic Steering
Anycast DNS advertises the same IPs from multiple edge locations, letting BGP route users to the nearest healthy endpoint. Providers combine Anycast with global server load balancing (GSLB) to steer requests by latency, geography, weight, or health.
Health Checks and Routing Policies
Use multi-vantage health checks (HTTP, TLS, and TCP) with aggressive detection and conservative recovery thresholds. Latency-based and geolocation rules reduce tail latency while allowing automated regional evacuation when checks fail. A SaaS platform can maintain sub-second failovers by pairing Anycast DNS with low TTLs and continuous synthetic monitoring.
Data Layer Consistency
Availability hinges on data design:
- Relational: Primary/replica with cross-region replication and controlled RPO/RTO; or multi-primary with conflict resolution at the application layer.
- NoSQL: Quorum writes/reads and tunable consistency for globally distributed workloads.
- Storage: Cross-region replication for objects and snapshots, plus region-isolated encryption keys.
Document and test RPO (data loss tolerance) and RTO (time to restore) per service.
Failover and DR Runbooks
- Detect: Health checks trigger alarms; incident commander is assigned.
- Isolate: Freeze writes or degrade features to protect data.
- Redirect: Update DNS/GSLB policy; validate with synthetic probes.
- Recover: Promote replicas, warm caches, and rehydrate queues.
- Back: Controlled failback when stability is proven.
Real-world: An e-commerce team uses Anycast DNS, latency policies, and Aurora Global Database for sub-minute read failover and guided write promotion in the secondary region.
Observability and Chaos
Define SLOs, track error budgets, and run synthetic probes from every continent. Schedule game days and chaos drills (inspired by Netflix’s Chaos Kong) to validate processes, TTLs, and automation.
Costs, Trade-offs, and Pitfalls
Budget for cross-region egress, duplicate environments, and operational overhead. Beware split-brain writes, long DNS TTLs, stateful sessions without sticky routing, and cache invalidation that lags replication. Build circuit breakers and feature flags to degrade gracefully instead of going dark.