Circuit Breaker Pattern (Resilience4j).

Purpose:

Prevents a service from repeatedly trying to call a failing downstream service, which could lead to resource exhaustion (cascading failure).

States:

1. CLOSED: Normal operation. Requests flow through.
2. OPEN: Downstream service is failing. Requests are rejected immediately (Fast-Fail).
3. HALF-OPEN: Periodically allows some requests to check if the downstream service has recovered.

Tooling:

Spring Boot typically uses Resilience4j (Hystrix is deprecated).