Fault Tolerance

The ability of a system to continue operating without interruption when one or more of its components fail.

Fault tolerance is the ability of a system to continue functioning correctly even when one or more of its components fail. A fault-tolerant system is designed to detect failures, isolate the faulty component, and continue operating -- possibly with reduced capacity -- without affecting the end user's experience.

Techniques for achieving fault tolerance include redundancy (running multiple instances of a component), replication (maintaining copies of data across nodes), health checks (detecting failed components), and circuit breakers (preventing cascading failures by stopping requests to unhealthy services). Graceful degradation is a related concept where a system provides reduced functionality rather than complete failure.

In API gateway and serverless architectures, fault tolerance is built into the platform at multiple levels. Edge-deployed gateways automatically route around failed nodes. Serverless functions are typically stateless and can be restarted instantly on healthy infrastructure. API gateways can implement retry logic, timeouts, and fallback responses to handle failures in upstream services, shielding clients from transient backend issues.