Circuit Breaker Pattern¶

When a downstream dependency fails repeatedly, stop attempting calls temporarily to prevent cascade failures, allow the dependency to recover, and fail fast to preserve system resources for requests that can succeed.

Tension Addressed¶

Simplicity vs. Resilience (adds complexity but prevents cascade failures)

Recognizable As¶

Three states (closed/open/half-open); failure thresholds; timeout periods; fallback behaviors; "service unavailable" responses that appear immediately rather than after timeout

Canonical Sources¶

Nygard, "Release It!" (2007, 2018); Fowler, "CircuitBreaker" pattern (2014)

Transfers To¶

Electrical Engineering (original concept), API Clients (client-side protection), Service Meshes (infrastructure-level protection), Mobile Apps (offline mode transitions)

The circuit breaker prevents the "thundering herd" problem where a failing service gets overwhelmed by retries. Named after electrical circuit breakers that protect against overcurrent, the pattern recognizes that sometimes the fastest failure is the best response.

Sub-concepts: - State Machine: Closed (normal), Open (failing fast), Half-Open (testing recovery) - Failure Detection: Count-based vs. rate-based thresholds