Performance Testing with k6: A Practical Guide

Performance issues in production are expensive. k6 makes it easy to find them before they impact users.

Why k6?

k6 stands out for several reasons:

• Write tests in JavaScript
• Low resource footprint
• Excellent metrics and reporting
• Easy CI/CD integration

Your First Load Test

import http from 'k6/http';
import { check, sleep } from 'k6';

export const options = {
  stages: [
    { duration: '1m', target: 50 },
    { duration: '3m', target: 50 },
    { duration: '1m', target: 0 },
  ],
};

export default function() {
  const res = http.get('https://api.example.com/products');
  check(res, { 'status is 200': (r) => r.status === 200 });
  sleep(1);
}

Understanding Metrics

Key metrics to watch:

• http_req_duration: Response time
• http_req_failed: Error rate
• vus: Virtual users
• iterations: Completed test cycles

Setting Thresholds

Fail tests when performance degrades:

export const options = {
  thresholds: {
    'http_req_duration': ['p95<500'],
    'http_req_failed': ['rate<0.01'],
  },
};

The best time to find performance issues is in testing, not from angry customer tickets.