k6-load-testing

# k6 Load Testing ## Overview k6 is a modern, developer-centric load testing tool that helps you write and execute performance tests for HTTP APIs, WebSocket endpoints, and browser scenarios. This skill provides comprehensive guidance on writing realistic load tests, configuring test scenarios (smoke, load, stress, spike, soak), analyzing results, and integrating with CI/CD pipelines. Use this skill when you need to validate system performance, identify bottlenecks, ensure SLA compliance, or catch performance regressions before deployment. --- ## When to Use This Skill - Use when you need to load test HTTP APIs, WebSocket endpoints, or browser scenarios - Use when setting up performance regression tests in CI/CD - Use when analyzing system behavior under various load conditions - Use when comparing performance between code changes - Use when validating SLA requirements and performance budgets --- ## k6 Basics ### Installation ```bash # macOS brew install k6 # Windows choco install k6 # Linux sudo gpg -k sudo gpg --no-default-keyring --keyring /usr/share/keyrings/k6-archive-keyring.gpg --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys C5AD17C747E3415A3642D57D77C6C491D6AC1D69 echo "deb [signed-by=/usr/share/keyrings/k6-archive-keyring.gpg] https://dl.k6.io/deb stable main" | sudo tee /etc/apt/sources.list.d/k6.list sudo apt-get update sudo apt-get install k6 ``` ### Quick Start ```javascript // simple-test.js import http from 'k6/http'; import { check, sleep } from 'k6'; export const options = { vus: 10, duration: '30s', }; export default function () { const res = http.get('https://httpbin.test.k6.io/get'); check(res, { 'status is 200': (r) => r.status === 200, 'response time < 500ms': (r) => r.timings.duration < 500, }); sleep(1); } ``` Run with: `k6 run simple-test.js` --- ## Test Configuration ### Common Options ```javascript export const options = { // Virtual Users (concurrent users) vus: 100, // Test duration duration: '5m', // Or use stages for ramp-up/ramp-down stages: [ { duration: '30s', target: 20 }, // Ramp up { duration: '1m', target: 100 }, // Stay at 100 { duration: '30s', target: 0 }, // Ramp down ], // Thresholds (SLA) thresholds: { http_req_duration: ['p(95)<500'], // 95% requests < 500ms http_req_failed: ['rate<0.01'], // Error rate < 1% }, // Load zones (distributed testing) ext: { loadimpact: { name: 'My Load Test', distribution: { 'amazon:us:ashburn': { weight: 50 }, 'amazon:eu: Dublin': { weight: 50 }, }, }, }, }; ``` ### Test Types | Type | Use Case | Configuration | |------|----------|---------------| | Smoke Test | Verify basic functionality | Low VUs (1-5), short duration | | Load Test | Normal expected load | Target VUs based on traffic | | Stress Test | Find breaking point | Ramp beyond capacity | | Spike Test | Sudden traffic spikes | Rapid increase/decrease | | Soak Test | Long-term stability | Extended duration | --- ## HTTP Testing ### Basic Requests ```javascript import http from 'k6/http'; import { check, sleep } from 'k6'; export default function () { // GET request const getRes = http.get('https://api.example.com/users'); check(getRes, { 'GET succeeded': (r) => r.status === 200, 'has users': (r) => r.json('data.length') > 0, }); // POST request with JSON body const postRes = http.post('https://api.example.com/users', JSON.stringify({ name: 'Test User', email: 'test@example.com' }), { headers: { 'Content-Type': 'application/json', 'Authorization': 'Bearer ' + __ENV.API_TOKEN, }, } ); check(postRes, { 'POST succeeded': (r) => r.status === 201, 'user created': (r) => r.json('id') !== undefined, }); sleep(1); } ``` ### Request Chaining ```javascript import http from 'k6/http'; import { check } from 'k6'; export default function () { // Login and extract token const loginRes = http.post('https://api.example.com/login', JSON.stringify({ email: 'test@example.com', password: 'password123' }) ); const token = loginRes.json('access_token'); // Use token in subsequent requests const headers = { 'Authorization': `Bearer ${token}`, 'Content-Type': 'application/json', }; const profileRes = http.get('https://api.example.com/profile', { headers: headers, }); check(profileRes, { 'profile loaded': (r) => r.status === 200, }); } ``` ### Parameterized Testing ```javascript import http from 'k6/http'; import { check } from 'k6'; const usernames = ['user1', 'user2', 'user3', 'user4', 'user5']; export default function () { // Use shared array with VU-specific index const username = usernames[__VU % usernames.length]; const res = http.get(`https://api.example.com/users/${username}`); check(res, { 'user found': (r) => r.status === 200, }); } ``` --- ## Browser Testing (k6 Browser) ```javascript import { browser } from 'k6/browser'; export const options = { scenarios: { browser_test: { executor: 'constant-vus', vus: 5, duration: '30s', browser: { type: 'chromium', }, }, }, }; export default async function () { const page = await browser.newPage(); try { await page.goto('https://example.com'); const title = await page.title(); console.log(`Page title: ${title}`); // Click and interact await page.click('button[data-testid="submit"]'); // Wait for response await page.waitForSelector('.success-message'); } finally { await page.close(); } } ``` Install browser support: `k6 install chromium` --- ## WebSocket Testing ```javascript import ws from 'k6/ws'; import { check } from 'k6'; export default function () { const url = 'wss://echo.websocket.org'; ws.connect(url, {}, function (socket) { socket.on('open', () => { console.log('WebSocket connected'); socket.send('Hello WebSocket'); }); socket.on('message', (data) => { console.log(`Received: ${data}`); check(data, { 'echo received': (d) => d.includes('Hello'), }); }); socket.on('close', () => { console.log('WebSocket closed'); }); // Send periodic messages socket.setInterval(function () { socket.send('ping'); }, 1000); // Close after 5 seconds socket.setTimeout(function () { socket.close(); }, 5000); }); } ``` --- ## Data Handling ### CSV Data Source ```javascript import http from 'k6/http'; import { check } from 'k6'; import { SharedArray } from 'k6/data'; // Option 1: Load once, shared across VUs const users = new SharedArray('users', function () { return open('./users.csv').split('\n').slice(1).map(line => { const [email, password] = line.split(','); return { email, password }; }); }); export default function () { const user = users[__VU % users.length]; const res = http.post('https://api.example.com/login', JSON.stringify({ email: user.email, password: user.password }) ); check(res, { 'login successful': (r) => r.status === 200 }); } ``` ### JSON Data Source ```javascript import http from 'k6/http'; import { check } from 'k6'; import { SharedArray } from 'k6/data'; const products = new SharedArray('products', function () { return JSON.parse(open('./products.json')); }); export default function () { const product = products[Math.floor(Math.random() * products.length)]; const res = http.get(`https://api.example.com/products/${product.id}`); check(res, { 'product found': (r) => r.status === 200 }); } ``` --- ## Thresholds & SLA ### Basic Thresholds ```javascript export const options = { vus: 50, duration: '2m', thresholds: { // Response time thresholds http_req_duration: ['p(95)<500', 'p(99)<1000'], // Error rate threshold http_req_failed: ['rate<0.01'], // Throughput threshold http_reqs: ['rate>100'], }, }; ``` ### Advanced Thresholds ```javascript export const options = { thresholds: { // Multiple thresholds on same metric http_req_duration: [ 'p(90)<300', // 90th percentile < 300ms 'p(95)<500', // 95th percentile < 500ms 'p(99)<1000', // 99th percentile < 1s 'avg<200', // average < 200ms ], // Custom metrics my_custom_metric: ['avg<100'], // Abort on threshold failure 'http_req_duration{method:GET}': ['p(95)<300'], }, }; ``` --- ## Custom Metrics ### Counters ```javascript import http from 'k6/http'; import { Counter, Trend, Rate, Gauge } from 'k6/metrics'; // Define custom metrics const myCounter = new Counter('api_calls_total'); const responseTime = new Trend('response_time'); const errorRate = new Rate('error_rate'); const activeUsers = new Gauge('active_users'); export default function () { const res = http.get('https://api.example.com/data'); // Increment counter myCounter.add(1); // Add to trend (for percentiles) responseTime.add(res.timings.duration); // Track error rate errorRate.add(res.status !== 200); // Set gauge value activeUsers.add(__VU); // Tagged metrics const taggedRes = http.get('https://api.example.com/users', {