Definition

A circuit breaker is a pattern where a system stops sending requests to a failing service for a period, allowing it to recover and preventing resource exhaustion.

Core concept

Modeled on electrical circuit breakers: if the number of recent failures (exceptions, timeouts) exceeds a threshold, the circuit opens, and calls fail immediately for a timeout period. After a while, a “half-open” trial allows some calls to test if recovery succeeded.

Use cases

Microservice architectures to prevent cascading failures. If Service B is down, Service A’s circuit breaker trips so that A doesn’t keep sending requests (which would time out), thus freeing threads for other tasks.

Trade-offs

Adds complexity; need tuning of thresholds and reset times.

Example

Netflix’s Hystrix library implements this: after e.g. 5 consecutive request failures, further calls fail fast.

References

Microservices design pattern (no direct cite in sources, but known concept).