Glossary
Circuit Breaker
A circuit breaker monitors calls to a dependency — a policy service, a downstream API — and, after enough failures in a row, stops sending new requests to it for a while rather than letting every caller keep hammering an already-struggling system. This gives the failing dependency room to recover instead of being buried under retries from every caller that hasn't yet noticed it's down.
Applied to an authorization dependency specifically, the circuit breaker's open state forces an explicit choice that fail-closed or fail-open design already has to answer: while the breaker is open and the real policy service isn't being called at all, does the caller deny by default, allow by default, or serve a cached decision. The circuit breaker changes when that fallback kicks in; it doesn't decide on its own what the fallback should be.