The Retry pattern and the Circuit Breaker pattern are complementary fault-tolerance mechanisms: Retry handles brief, transient failures, while Circuit Breaker protects the system once failures become persistent.
Key Points: • The Retry pattern automatically re-attempts a failed call, often with backoff, on the assumption that many failures are short-lived, like a momentary network blip. • The Circuit Breaker pattern tracks the failure rate of calls to a dependency and stops sending requests entirely once that rate crosses a threshold. • Without a circuit breaker, blind retries against a genuinely down service can make things worse by piling on more load exactly when the service needs to recover. • Combined, retries handle the common case of transient errors, while the circuit breaker acts as a safety net that kicks in once retries aren't helping, stopping further attempts. • Retries are usually applied per call, while the circuit breaker tracks state across many calls to the same dependency over a rolling window.
Example: A call to a Payment service that fails once might succeed on an automatic retry a few hundred milliseconds later due to a transient blip, but if failures keep happening across many calls, the circuit breaker opens and stops further retries from being attempted at all, protecting both the caller and the struggling service.
Interview Tip: A concise interview answer is:
"Retry handles short-lived, transient failures by trying again, usually with backoff, while the circuit breaker watches the failure rate across many calls and stops all further attempts, retries included, once a dependency is clearly struggling. They work together: retry absorbs blips, and the circuit breaker prevents retries from making a real outage worse."