implement-a-circuit-breaker

name	implement-a-circuit-breaker
category	code
description	Implement a circuit breaker with meaningful failure classification, bounded state, safe fallback, probing, recovery, and observability. Use when repeated dependency calls can amplify an outage.

implement-a-circuit-breaker

When to use

• Use around a dependency whose failure can consume scarce resources or cascade.
• Do not count caller cancellation or valid business rejection as dependency failure.

Preconditions

• Define operation, timeout, failures, volume, fallback, retry, idempotency, and recovery.

Procedure

1. Classify success, slow, retryable, terminal, caller, and dependency outcomes.
2. Choose scope by operation, tenant, region, or endpoint without global collateral damage.
3. Define closed, open, and half-open transitions with minimum volume and bounded windows.
4. Coordinate timeout, retry, concurrency, and backoff.
5. Provide a truthful safe fallback or explicit unavailability.
6. Test flapping, low volume, partial failure, probe concurrency, and restart state.

Failure plan

• Allow authorized bounded bypass only with monitoring and resource protection.

Worked example

A payment breaker opens on upstream timeouts but not declined cards and permits one idempotent probe.

Done

• A circuit-breaker implementation records scope, classifications, thresholds, states, fallback, and telemetry
• Low-volume, timeout, retry, probe, flapping, restart, bypass, and idempotency tests verify behavior