Circuit Breaker diagram template

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About this design

A failing dependency is dangerous mostly because callers keep waiting on it. Threads pile up behind slow requests, the caller exhausts its own capacity, and a small outage cascades upward. A circuit breaker wraps the call and counts failures. While the circuit is closed, requests flow normally. When failures cross a threshold the circuit opens and calls fail immediately, with no waiting, returning a cached value or a degraded response instead. After a cool-down the breaker moves to half open and lets a few trial requests through; success closes it again, failure reopens it. This template shows the caller, the breaker, the protected service and a fallback. Discuss thresholds based on error rate rather than count, bulkheads that cap concurrency per dependency, timeouts that are shorter than the user's patience, and alerting when a breaker opens.

Diagram as text

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title "Circuit breaker"
direction LR
service caller "Caller" -> service cb "Circuit breaker"
cb -[closed]-> microservice dep "Payments service"
cb -[open: fail fast]-> cache redis "Fallback response"
cb -> monitor prometheus "State metrics"
cb -[half-open probes]-> dep