/k6-performance

name: k6-performance
description: Performance and load testing skill using k6, covering load test scripts, thresholds, scenarios, checks, custom metrics, and results analysis.
license: MIT
metadata:
  author: thetestingacademy
  version: 1.0.0
  source: https://qaskills.sh/skills/thetestingacademy/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: 'user@example.com',
      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
}

Test Types

Smoke Test

export const options = {
  vus: 1,
  duration: '1m',
  thresholds: {
    http_req_duration: ['p(99)<1500'],
    http_req_failed: ['rate<0.01'],
  },
};

// Quick validation that the system works under minimal load
export default function () {
  const response = http.get(`${BASE_URL}/api/health`);
  check(response, {
    'status is 200': (r) => r.status === 200,
  });
  sleep(1);
}

Load Test

export const options = {
  stages: [
    { duration: '5m', target: 100 },   // Ramp up
    { duration: '10m', target: 100 },   // Steady state
    { duration: '5m', target: 0 },      // Ramp down
  ],
  thresholds: {
    http_req_duration: ['p(95)<500'],
    http_req_failed: ['rate<0.01'],
  },
};

Stress Test

export const options = {
  stages: [
    { duration: '2m', target: 100 },
    { duration: '5m', target: 100 },
    { duration: '2m', target: 200 },
    { duration: '5m', target: 200 },
    { duration: '2m', target: 300 },
    { duration: '5m', target: 300 },
    { duration: '2m', target: 400 },
    { duration: '5m', target: 400 },
    { duration: '10m', target: 0 },
  ],
  thresholds: {
    http_req_duration: ['p(95)<1000'],
    http_req_failed: ['rate<0.05'],
  },
};

Spike Test

export const options = {
  stages: [
    { duration: '1m', target: 10 },     // Normal load
    { duration: '10s', target: 500 },    // Spike!
    { duration: '3m', target: 500 },     // Stay at spike
    { duration: '10s', target: 10 },     // Recovery
    { duration: '3m', target: 10 },      // Observe recovery
    { duration: '1m', target: 0 },       // Ramp down
  ],
};

Soak Test

export const options = {
  stages: [
    { duration: '5m', target: 50 },     // Ramp up
    { duration: '4h', target: 50 },     // Sustained load for 4 hours
    { duration: '5m', target: 0 },      // Ramp down
  ],
  thresholds: {
    http_req_duration: ['p(95)<500'],
    http_req_failed: ['rate<0.01'],
  },
};

Scenarios (Advanced Configuration)

export const options = {
  scenarios: {
    browse_products: {
      executor: 'ramping-vus',
      startVUs: 0,
      stages: [
        { duration: '2m', target: 50 },
        { duration: '5m', target: 50 },
        { duration: '2m', target: 0 },
      ],
      gracefulRampDown: '30s',
      exec: 'browseProducts',
    },
    checkout_flow: {
      executor: 'constant-arrival-rate',
      rate: 10,          // 10 iterations per timeUnit