Backend & systems·Resilience and failure handling
you reject the request immediately when you already know the dependency is down, instead of making the caller wait for a timeout.
Fail fast
Returning an error as soon as failure is certain rather than proceeding hopefully. It frees the caller's resources and keeps queues from filling with doomed work. It is the behaviour a circuit breaker implements, and it is why validating inputs before doing expensive work is a resilience decision, not just a tidiness one.