K6 Load Testing Cheatsheet

What is K6?

K6 is a modern, developer-friendly load testing tool built for testing the performance of APIs, microservices, and websites. Write tests in JavaScript and run them from the CLI or CI/CD pipeline.

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📥 K6 - Installation

Install K6 on different operating systems.

macOS

brew install k6

Linux (Debian / Ubuntu)

sudo apt update
sudo apt install k6

Windows

choco install k6

Verify installation:

k6 version

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🚀 K6 - Basic Test Script

Minimal HTTP load test example.

import http from 'k6/http';
import { sleep } from 'k6';

export default function () {
  http.get('https://test.k6.io');
  sleep(1);
}

Run:

k6 run script.js

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👥 K6 - Virtual Users & Duration

Control load using VUs and duration.

k6 run --vus 10 --duration 30s script.js

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📊 K6 - Stages (Ramp Up / Down)

Simulate realistic traffic patterns.

export const options = {
  stages: [
    { duration: '30s', target: 10 },
    { duration: '1m', target: 50 },
    { duration: '30s', target: 0 }
  ],
};

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🎯 K6 - Thresholds (SLAs / SLOs)

Fail tests if performance criteria are breached.

export const options = {
  thresholds: {
    http_req_duration: ['p(95)<500'],
    http_req_failed: ['rate<0.01'],
  },
};

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✅ K6 - Checks (Assertions)

Validate responses during load.

import { check } from 'k6';

check(res, {
  'status is 200': (r) => r.status === 200,
  'response time < 500ms': (r) => r.timings.duration < 500,
});

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🌐 K6 - HTTP Methods

http.get(url);
http.post(url, payload, params);
http.put(url, payload);
http.del(url);

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🔐 K6 - Headers & Authentication

const params = {
  headers: {
    'Authorization': 'Bearer TOKEN',
    'Content-Type': 'application/json',
  },
};

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🔧 K6 - Environment Variables

k6 run -e BASE_URL=https://api.test.com script.js

const baseUrl = __ENV.BASE_URL;

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📝 K6 - Data Parameterization

import data from './users.json';

export default function () {
  const user = data[Math.floor(Math.random() * data.length)];
}

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⚙️ K6 - Executors (Advanced)

export const options = {
  scenarios: {
    constant_load: {
      executor: 'constant-vus',
      vus: 20,
      duration: '1m',
    },
  },
};

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💪 K6 - Stress Testing

stages: [
  { duration: '1m', target: 50 },
  { duration: '1m', target: 200 },
  { duration: '30s', target: 0 },
]

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⚡ K6 - Spike Testing

stages: [
  { duration: '10s', target: 200 },
  { duration: '1m', target: 0 },
]

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⏱️ K6 - Soak Testing

{ duration: '2h', target: 50 }

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📄 K6 - Output to JSON

k6 run --out json=results.json script.js

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📊 K6 - InfluxDB Integration

k6 run --out influxdb=http://localhost:8086/k6 script.js

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🔄 K6 - CI/CD Usage

k6 run script.js || exit 1

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📈 K6 - Common Metrics

Metric	Description
http_req_duration	Total request time
http_req_failed	Failed request rate
vus	Active virtual users
checks	Assertion results

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🐛 K6 - Debugging

k6 run --http-debug="full" script.js

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✅ K6 - Best Practices Checklist

• Define clear SLAs
• Add thresholds
• Use realistic data
• Monitor backend metrics
• Fail CI on performance breach

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