Performance Testing with k6 or autocannon

APIs pass functional tests but fail under load. Performance regressions are discovered in production rather than during development.

Use k6 or autocannon for load testing as part of CI or pre-release checks.

// k6 load test script (k6.io)
import http from 'k6/http';
import { check, sleep } from 'k6';

export const options = {
  stages: [
    { duration: '30s', target: 10 },   // Ramp up to 10 VUs
    { duration: '1m', target: 10 },    // Stay at 10 VUs
    { duration: '10s', target: 0 },    // Ramp down
  ],
  thresholds: {
    http_req_duration: ['p(95)<500'],  // 95% of requests < 500ms
    http_req_failed: ['rate<0.01'],    // Error rate < 1%
  },
};

export default function() {
  const res = http.get('http://localhost:3000/api/users');
  check(res, {
    'status is 200': (r) => r.status === 200,
    'response time < 200ms': (r) => r.timings.duration < 200,
  });
  sleep(1);
}

// Run: k6 run script.js

# autocannon for quick HTTP benchmarking
npx autocannon -c 100 -d 30 http://localhost:3000/api/users
# -c: concurrent connections
# -d: duration in seconds

Load testing reveals performance characteristics that unit tests cannot: database connection pool exhaustion, memory leaks under sustained load, and response time degradation at scale.