Circuit breaker pattern for external API dependencies

When an external API — payment gateway, SMS provider, identity service — starts returning errors, repeated synchronous retries amplify load on an already-struggling service and cascade failures throughout your application. CWE-703 (improper check for exceptional conditions) applies to this failure mode. ISO 25010 reliability.fault-tolerance requires the system to degrade gracefully under component failures; a missing circuit breaker means one downstream outage can freeze all request-handling threads or queue workers indefinitely, taking down your entire service.

Use the opossum library for Node.js or implement a minimal hand-rolled breaker for fetch-based calls. The breaker must track failure rate and reject calls when the circuit is open.

// lib/circuit-breaker.ts
import CircuitBreaker from 'opossum'

export function createBreaker<T>(fn: (...args: unknown[]) => Promise<T>) {
  return new CircuitBreaker(fn, {
    timeout: 5000,       // fail after 5s
    errorThresholdPercentage: 50, // open at 50% failure rate
    resetTimeout: 30000, // retry after 30s
  })
}

// Usage:
const breaker = createBreaker(callPaymentAPI)
const result = await breaker.fire(payload)

Wrap the three highest-traffic external integrations first: payment, auth, and any real-time data feed.