Designing Highly Available Web Applications
High availability means your web application stays up and responsive even when parts fail. It reduces user friction, preserves trust, and lowers downtime costs. Achieving it requires careful architecture, reliable infrastructure, and disciplined operations.
Core principles
- Redundancy across layers (compute, storage, regions) to survive failures.
- Stateless services so any instance can handle requests.
- Automated health checks and fast failover to reroute traffic quickly.
- Observability with metrics, logs, and traces to detect issues early.
- Graceful degradation so vital features stay up even if noncritical parts fail.
Practical patterns
- Global load balancing and health checks to route users to healthy regions.
- Multi-region data replication and caching to reduce latency and maintain availability.
- Regular backups and tested disaster recovery plans to recover data fast.
- Externalized session state and distributed caches to keep apps responsive.
Operational practices
Keep recovery in mind during deployments. Run fault-injection drills, maintain clear runbooks, and monitor MTTR. Automate rollback when needed and review incidents to improve resilience.
Key Takeaways
- Design for redundancy and statelessness.
- Monitor and rehearse failover to shorten recovery time.
- Align architecture and processes with expected SLAs and user needs.