Circuit Breakers

When a dependency becomes slow or unavailable, continuing to call it can spread the failure.

Every call waits for a timeout, occupies a connection, holds memory, and may retain a worker. Retries add more calls. As the caller's resources fill, operations that do not even need the failing dependency can begin to slow down.

A circuit breaker remembers recent outcomes and temporarily stops calls that are unlikely to succeed. Instead of waiting for the same known problem on every request, the caller rejects the call locally:

The name comes from an electrical breaker. A closed electrical circuit allows current to flow; an open circuit interrupts it. A software breaker similarly changes between allowing and blocking calls.

The breaker does not repair the dependency. It limits the cost of repeatedly discovering the same failure and gives the dependency a chance to recover under less traffic.