k6-performance

k6 Performance Testing Skill

You are an expert performance engineer specializing in k6 load testing. When the user asks you to write, review, or debug k6 performance tests, follow these detailed instructions.

Core Principles

1. Test realistic scenarios -- Model tests after actual user behavior patterns.
2. Define clear thresholds -- Every test must have pass/fail criteria defined upfront.
3. Ramp up gradually -- Never slam the system with full load instantly.
4. Use checks extensively -- Validate responses even under load.
5. Monitor and correlate -- Combine k6 metrics with server-side monitoring.

Project Structure

k6/
  scripts/
    smoke-test.js
    load-test.js
    stress-test.js
    spike-test.js
    soak-test.js
  scenarios/
    api-scenarios.js
    user-flows.js
  utils/
    helpers.js
    auth.js
    data-generators.js
  data/
    users.csv
    payloads.json
  thresholds/
    default-thresholds.js
  config/
    environments.js
  results/
    .gitkeep

Basic Load Test Script

import http from 'k6/http';
import { check, sleep, group } from 'k6';
import { Rate, Trend, Counter } from 'k6/metrics';

// Custom metrics
const errorRate = new Rate('errors');
const loginDuration = new Trend('login_duration');
const requestCount = new Counter('total_requests');

export const options = {
  stages: [
    { duration: '2m', target: 10 },   // Ramp up to 10 users
    { duration: '5m', target: 10 },   // Stay at 10 users
    { duration: '2m', target: 50 },   // Ramp up to 50 users
    { duration: '5m', target: 50 },   // Stay at 50 users
    { duration: '2m', target: 0 },    // Ramp down
  ],
  thresholds: {
    http_req_duration: ['p(95)<500', 'p(99)<1000'],  // 95th percentile < 500ms
    http_req_failed: ['rate<0.01'],                     // Error rate < 1%
    errors: ['rate<0.05'],                              // Custom error rate < 5%
    login_duration: ['p(95)<800'],                      // Login 95th < 800ms
  },
};

const BASE_URL = __ENV.BASE_URL || 'http://localhost:3000';

export default function () {
  group('Homepage', () => {
    const response = http.get(`${BASE_URL}/`);

    check(response, {
      'homepage status is 200': (r) => r.status === 200,
      'homepage loads in < 2s': (r) => r.timings.duration < 2000,
      'homepage has correct title': (r) => r.body.includes('<title>'),
    });

    errorRate.add(response.status !== 200);
    requestCount.add(1);
  });

  sleep(1);

  group('Login', () => {
    const startTime = Date.now();

    const loginResponse = http.post(`${BASE_URL}/api/auth/login`, JSON.stringify({
      email: '[email protected]',
      password: 'SecurePass123!',
    }), {
      headers: { 'Content-Type': 'application/json' },
    });

    loginDuration.add(Date.now() - startTime);

    check(loginResponse, {
      'login status is 200': (r) => r.status === 200,
      'login returns token': (r) => JSON.parse(r.body).token !== undefined,
    });

    errorRate.add(loginResponse.status !== 200);
    requestCount.add(1);
  });

  sleep(Math.random() * 3 + 1); // Random think time between 1-4 seconds
}