k6 Load Testing Expert

Expert in performance testing with k6 framework.

Core k6 Principles

• Virtual Users (VUs): Each VU runs the test script independently in parallel
• Iterations vs Duration: Choose between iteration-based or time-based test execution
• Stages: Gradually ramp up/down load to simulate realistic traffic patterns
• Thresholds: Define pass/fail criteria for automated performance validation
• Metrics: Focus on key performance indicators (response time, throughput, error rate)

Basic Test Script Structure

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

// Custom metrics
const errorRate = new Rate('errors');
const customTrend = new Trend('custom_duration');

// Test configuration
export const options = {
  stages: [
    { duration: '2m', target: 10 },  // Ramp up to 10 users
    { duration: '5m', target: 10 },  // Stay at 10 users
    { duration: '2m', target: 20 },  // Ramp up to 20 users
    { duration: '5m', target: 20 },  // Stay at 20 users
    { duration: '2m', target: 0 },   // Ramp down to 0
  ],
  thresholds: {
    http_req_duration: ['p(95)<500'],  // 95% of requests under 500ms
    http_req_failed: ['rate<0.1'],     // Error rate under 10%
    errors: ['rate<0.1'],
  },
};

// Setup function (runs once before test)
export function setup() {
  // Prepare test data, authenticate, etc.
  const loginRes = http.post('https://api.example.com/auth/login', {
    email: '[email protected]',
    password: 'password123',
  });

  return { token: loginRes.json('token') };
}

// Main test function (runs for each VU)
export default function(data) {
  const params = {
    headers: {
      'Authorization': `Bearer ${data.token}`,
      'Content-Type': 'application/json',
    },
  };

  const response = http.get('https://api.example.com/users', params);

  // Verify response
  check(response, {
    'status is 200': (r) => r.status === 200,
    'response time < 500ms': (r) => r.timings.duration < 500,
    'response body contains users': (r) => r.body.includes('users'),
  });

  // Track custom metrics
  errorRate.add(response.status !== 200);
  customTrend.add(response.timings.duration);

  // Think time between requests
  sleep(Math.random() * 2 + 1); // 1-3 seconds
}

// Teardown function (runs once after test)
export function teardown(data) {
  // Cleanup operations
  console.log('Test completed');
}

Test Scenario Patterns

Load Test (Normal Traffic)

export const options = {
  stages: [
    { duration: '5m', target: 50 },   // Ramp up
    { duration: '30m', target: 50 },  // Steady state
    { duration: '5m', target: 0 },    // Ramp down
  ],
  thresholds: {
    http_req_duration: ['p(95)<200', 'p(99)<500'],
    http_req_failed: ['rate<0.01'],
  },
};

Stress Test (Beyond Normal Capacity)

export const options = {
  stages: [
    { duration: '2m', target: 100 },
    { duration: '5m', target: 100 },
    { duration: '2m', target: 200 },
    { duration: '5m', target: 200 },
    { duration: '2m', target: 300 },  // Beyond normal capacity
    { duration: '5m', target: 300 },
    {