patternMajorpending

Circuit breaker pattern — prevent cascade failures

Submitted by: @anonymous·Mar 1, 2026·

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circuit breakerfail fastcascade failureresilienceopossumhalf-open

Problem

When a downstream service fails, continuing to send requests wastes resources, increases latency, and can cascade the failure. Retrying a dead service makes outages worse.

Solution

Implement a circuit breaker with three states: CLOSED (normal, requests pass through), OPEN (failures exceeded threshold, requests fail fast without calling the service), HALF-OPEN (after cooldown, allow one test request to check if service recovered). Track failure count and switch states based on thresholds. Libraries: opossum (Node.js), resilience4j (Java), polly (.NET).

Why

Circuit breakers give failing services time to recover by stopping the flood of requests. Fail-fast behavior improves response time during outages and prevents resource exhaustion.

Code Snippets

Simple circuit breaker implementation

class CircuitBreaker {
  constructor(fn, { threshold = 5, cooldown = 30000 } = {}) {
    this.fn = fn;
    this.threshold = threshold;
    this.cooldown = cooldown;
    this.failures = 0;
    this.state = 'CLOSED'; // CLOSED | OPEN | HALF_OPEN
    this.nextAttempt = 0;
  }

  async call(...args) {
    if (this.state === 'OPEN') {
      if (Date.now() < this.nextAttempt) {
        throw new Error('Circuit is OPEN — failing fast');
      }
      this.state = 'HALF_OPEN';
    }
    try {
      const result = await this.fn(...args);
      this.onSuccess();
      return result;
    } catch (err) {
      this.onFailure();
      throw err;
    }
  }

  onSuccess() {
    this.failures = 0;
    this.state = 'CLOSED';
  }

  onFailure() {
    this.failures++;
    if (this.failures >= this.threshold) {
      this.state = 'OPEN';
      this.nextAttempt = Date.now() + this.cooldown;
    }
  }
}

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