K6 Tutorial: How To Use K6 For Load Testing

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K6 Tutorial: How to Use K6 for Load Testing

Hey guys! 👋 Today, we're diving deep into K6, a fantastic open-source load testing tool. If you're looking to ensure your web applications can handle the pressure, you've come to the right place. We'll cover everything from installation to writing your first test script, so buckle up and let's get started!

What is K6?

Before we jump into the how-to, let's quickly understand what K6 is all about. K6 is a modern load testing tool engineered for developers and DevOps teams. Unlike traditional tools, K6 is designed to be developer-friendly, using JavaScript for scripting tests. This makes it easy for developers to write and understand load tests without having to learn a new language or deal with complex configurations. K6 is also built for automation and integration with your CI/CD pipelines, allowing you to catch performance issues early in the development lifecycle. It supports various protocols, including HTTP, WebSockets, and gRPC, making it versatile for testing different types of applications. Plus, it's open-source, meaning you get a powerful tool without breaking the bank! One of the key advantages of K6 is its focus on performance and scalability. It's written in Go and designed to handle high loads with minimal resource consumption. This makes it suitable for simulating real-world traffic scenarios and identifying bottlenecks in your system. K6 provides detailed metrics and insights into your application's performance, helping you optimize your code and infrastructure. With K6, you can shift-left your performance testing, ensuring that your applications are always ready to handle the load.

Installation

Alright, first things first: let's get K6 installed. The installation process varies depending on your operating system, but don't worry, it's generally straightforward. Here's a breakdown for the most common platforms:

macOS

If you're on a Mac, Homebrew is your best friend. Just open your terminal and run:

brew install k6

Once it's done, verify the installation by typing k6 version in your terminal. You should see the installed version number.

Linux

For Linux users, there are a couple of options. You can use apt (for Debian/Ubuntu-based systems) or download a pre-built binary.

Using apt:

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 379CE192D401AB61
echo "deb 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

Downloading the binary:

Go to the official K6 website (https://k6.io/docs/getting-started/installation/) and grab the appropriate binary for your system architecture. Extract the archive and add the K6 binary to your PATH.

Windows

Windows users can download a pre-built binary from the K6 website. After downloading, extract the archive and add the K6 directory to your system's PATH environment variable. This will allow you to run K6 from any command prompt.

Docker

If you prefer using Docker, K6 provides an official Docker image. You can pull it from Docker Hub:

docker pull grafana/k6

To run K6 in a Docker container, you'll mount your test script into the container and execute it.

Writing Your First K6 Test

Now that we have K6 installed, let's write our first test script. K6 uses JavaScript (ES6) for scripting, so you should feel right at home if you're a web developer. Create a new file named script.js and add the following code:

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

export const options = {
  vus: 10, // Virtual users
  duration: '30s', // Test duration
};

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

Let's break down this script:

  • import http from 'k6/http';: Imports the HTTP module, which allows us to make HTTP requests.
  • import { sleep } from 'k6';: Imports the sleep function, which pauses the execution for a specified duration.
  • export const options = { ... };: Defines the test configuration, such as the number of virtual users (VUs) and the test duration. Here, we're simulating 10 virtual users for 30 seconds.
  • export default function () { ... };: The main function that K6 executes. In this case, it sends a GET request to https://test.k6.io and then pauses for 1 second.

Running Your K6 Test

With our script ready, it's time to run the test. Open your terminal, navigate to the directory containing script.js, and run the following command:

k6 run script.js

K6 will start executing the test and display real-time metrics in the terminal. You'll see information such as the number of requests, response times, and error rates. This is your first glimpse into how your application performs under load!

If you're using Docker, you can run the test with the following command:

docker run -i --rm -v $(pwd):/app grafana/k6 run /app/script.js

Understanding K6 Options

K6 offers a variety of options to configure your tests. Let's explore some of the most commonly used ones:

  • vus: Specifies the number of virtual users to simulate. This determines the concurrency of your test.
  • duration: Sets the total duration of the test. K6 will run the test for this amount of time.
  • iterations: Defines the number of iterations each virtual user should perform. This is useful when you want to run a specific number of requests.
  • rps: Stands for requests per second. This limits the number of requests K6 will send per second.
  • stages: Allows you to define a ramp-up or ramp-down scenario. You can gradually increase or decrease the number of virtual users over time.

Here's an example of using stages:

export const options = {
  stages: [
    { duration: '10s', target: 10 }, // Ramp up to 10 VUs over 10 seconds
    { duration: '20s', target: 10 }, // Stay at 10 VUs for 20 seconds
    { duration: '10s', target: 0 },  // Ramp down to 0 VUs over 10 seconds
  ],
};

Advanced K6 Features

K6 has a ton of advanced features to help you create more sophisticated load tests. Here are a few highlights:

Checks and Thresholds

Checks and thresholds allow you to validate the results of your tests and ensure that your application meets specific performance criteria. Checks are simple assertions that verify a condition is true, while thresholds define acceptable performance ranges.

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

export const options = {
  vus: 10,
  duration: '30s',
  thresholds: {
    http_req_duration: ['p95<500'], // 95th percentile response time must be less than 500ms
    http_req_failed: ['rate<0.01'], // Error rate must be less than 1%
  },
};

export default function () {
  const res = http.get('https://test.k6.io');
  check(res, { 'status is 200': (r) => r.status === 200 });
  sleep(1);
}

Data Parameterization

Data parameterization allows you to use different input data for each virtual user or iteration. This is useful for simulating real-world scenarios where users interact with your application in different ways. K6 supports reading data from CSV files or generating it dynamically.

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

const data = new SharedArray('users', function () {
  // Load data from a CSV file
  return JSON.parse(open('./users.json'));
});

export const options = {
  vus: 10,
  duration: '30s',
};

export default function () {
  const user = data[Math.floor(Math.random() * data.length)];
  const res = http.get(`https://test.k6.io/user/${user.id}`);
  sleep(1);
}

Modules and Extensions

K6 supports modules and extensions, allowing you to extend its functionality and integrate with other tools. You can use existing modules or create your own to add custom logic to your tests.

Best Practices for K6 Load Testing

To get the most out of K6, here are some best practices to keep in mind:

  • Start small: Begin with a small number of virtual users and gradually increase the load to identify bottlenecks.
  • Simulate real-world scenarios: Design your tests to mimic how real users interact with your application.
  • Monitor your infrastructure: Keep an eye on your server resources (CPU, memory, disk I/O) during the test to identify performance issues.
  • Use checks and thresholds: Define clear performance criteria and use checks and thresholds to validate your results.
  • Automate your tests: Integrate K6 into your CI/CD pipeline to catch performance issues early.

Conclusion

And there you have it! You've now got a solid foundation for using K6 to load test your web applications. Remember, performance testing is an ongoing process. Keep experimenting, keep learning, and keep optimizing! Happy testing, folks! 🎉