The original title is: "Stop calling a service that's already down: circuit breakers with Resilience4j"

Short summary

Circuit breakers prevent cascade failures by stopping calls to struggling services and returning fast fallbacks instead. Resilience4j provides a lightweight Spring Boot implementation with three states—CLOSED (normal), OPEN (protecting), and HALF-OPEN (probing)—configured by failure-rate threshold and minimum-call counts. Implement with @CircuitBreaker annotations and cheap fallbacks; tune configuration differently for dev (short windows, fast recovery) versus prod (stable windows, longer cooldown).

• •Circuit breaker stops calling failing dependencies, returning degraded fallbacks instead of propagating outages
• •Three-state machine (CLOSED→OPEN→HALF-OPEN) isolates problems and self-heals when dependencies recover
• •Configure with failure-rate threshold, sliding-window size, and wait duration; tune per environment

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