When you’re running multiple services in production, failures are unavoidable. A downstream service might spike latency, return 500s, or disappear entirely. Without protection, a single fault can cascade across your system, wasting threads, exhausting connection pools, and eventually taking down dependent services. This is where circuit breakers shine—they degrade gracefully instead of amplifying failure.
You’ve probably used timeouts and retries, but those alone aren’t enough. Retries exacerbate overload, and timeouts still waste resources waiting. A circuit breaker monitors failures, and when they cross a threshold, it short-circuits the call, returning a predefined fallback immediately. This stops your service from burning CPU on doomed requests and lets downstream recover under reduced load.
The state machine is simple: closed (normal operation), open (rejecting requests), and half-open (probing for recovery). In closed state, every call is passed through; failures increment a counter. If the failure ratio exceeds your threshold (e.g., 50% of the last 10 calls), it trips to open. In open state, calls fail fast without reaching the remote service. After a configurable timeout, it moves to half-open and allows a few probes—if they succeed, it resets to closed; if not, it goes back to open.
