Circuit Breaker Pattern

Protects a system from cascading failures by monitoring calls to an external dependency. When failures exceed a threshold, the circuit "trips" — subsequent calls fail immediately without attempting the operation, giving the dependency time to recover.

Like an electrical circuit breaker: when current spikes (failures accumulate), the breaker opens to prevent damage. It then probes for recovery before restoring normal flow.

When to Use

• Calling external APIs, databases, third-party services, or microservices
• Any dependency that can be slow or unavailable — not just HTTP calls
• Systems where one failing service should not bring down the whole application
• High-traffic services where queuing up failed requests causes cascading load

Don't use for:

• Local in-process function calls (no network boundary, no circuit breaker needed)
• Operations that must succeed or retry indefinitely (use retry + timeout instead)
• User-facing validation errors (4xx responses are not failures — they are expected)