Always-On Web Architecture: Multi-Region, Anycast DNS, Failover, Backups & Incident Response
Posted: September 16, 2025 to Announcements.
High-Availability Web Architecture: Multi-Region Hosting, Anycast DNS, Failover, Backups, and Incident Response
When every minute of downtime costs users and revenue, “high availability” means designing systems that keep serving traffic despite failures. The aim is predictable uptime, low latency, and explicit recovery objectives (RTO/RPO) that the business accepts.
Multi-Region Hosting
Run your application in at least two regions to survive a regional outage and to serve users closer to where they are. Choose between active-active (all regions serve traffic) and active-passive (a hot standby takes over). Active-active improves latency and capacity but needs rigorous data consistency plans; active-passive is simpler but risks stale capacity assumptions.
- Replicate data with managed cross-region databases or message queues; prefer asynchronous replication with clear RPOs.
- Use global load balancers with health checks to steer users to healthy regions.
- Keep state externalized (session stores, object storage) to enable stateless app tiers.
Example: An e-commerce platform runs US-East and EU-West. A power event in EU-West removes a zone; traffic shifts to US-East within seconds, orders continue, and EU-West drains when healthy.
Anycast DNS
Authoritative DNS served from anycasted nameservers routes queries to the nearest edge, reducing latency and absorbing DDoS. Combine short, realistic TTLs with health-checked records or traffic policies (geo, latency, weighted) to route around failures automatically.
Example: A media site fronted by anycast DNS and a global CDN keeps resolving during a regional attack; users are transparently directed to alternate POPs and origins.
Failover Strategies
- Automated failover via health checks at L4/L7; aim for sub-minute detection, careful to avoid flapping.
- Database promotion with fencing and split-brain protection; rehearse application reconfiguration.
- Graceful degradation: serve cached pages, limit features, or shed noncritical traffic.
- Progressive delivery (canary, feature flags) to limit blast radius during releases.
Example: A fintech fails over its API from eu-central to us-east when latency SLOs breach; write traffic pauses for 30 seconds while the replica promotes, then resumes within RPO.
Backups and Data Continuity
- Daily snapshots plus point-in-time recovery; store copies in a separate account and region.
- Immutability (object lock, WORM) and encryption with rotated keys.
- Quarterly restore drills with measured RTO/RPO and checklist sign-offs.
Example: After accidental table drops, a SaaS restores to a clean snapshot and replays logs to within 5 minutes of loss.
Incident Response
- Detect: SLO-based alerts, synthetic probes, and user-visible dashboards.
- Stabilize: trigger failover runbooks, enact rate limits, enable read-only modes.
- Communicate: status page, in-app banners, and stakeholder updates at set intervals.
- Recover: backfill data, rehydrate caches, and revert mitigations.
- Learn: blameless review and chaos tests to verify fixes.