k6: Virtual Users, Checks & Thresholds

k6 is an open-source load testing tool for testing API/website performance and reliability under simulated traffic. Test scripts are written in familiar JavaScript, but executed via a fast Go-based runtime -- meaningfully more efficient than spawning a full browser or Node.js process per simulated user.

A Basic Test Script

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

export const options = {
  vus: 50,        // 50 concurrent virtual users
  duration: '30s',
}

export default function () {
  const res = http.get('https://test.example.com/api/products')

  // check() records pass/fail WITHOUT stopping the test -- the load
  // test keeps generating traffic regardless of individual failures
  check(res, {
    'status is 200': (r) => r.status === 200,
    'response has products': (r) => JSON.parse(r.body).length > 0,
  })

  // Simulates realistic 'think time' between requests, rather than
  // hammering the target as fast as technically possible
  sleep(1)
}

Thresholds: Automated Pass/Fail for CI

export const options = {
  vus: 50,
  duration: '30s',
  thresholds: {
    // k6 exits with a non-zero status if breached -- lets a CI
    // pipeline automatically fail the build on a regression
    http_req_duration: ['p(95)<500'],  // 95% of requests under 500ms
    http_req_failed: ['rate<0.01'],    // error rate under 1%
  },
}

Running Tests

k6 run script.js

# Override options from the command line for quick ad-hoc adjustments
k6 run --vus 100 --duration 1m script.js