K6 Websocket Example: How to Use Websockets with K6 for Load Testing

Websockets are an excellent way to achieve real-time communication between clients and servers. They are particularly useful for building applications that require continuous updates, such as chat applications or real-time dashboards. In this article, we will explore how to use websockets with K6 for load testing. We will cover the following topics:

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What is K6?

K6 is an open-source load testing tool designed for developers. It allows you to write tests in JavaScript and execute them locally or in the cloud. K6 is built on top of the Go language, which makes it fast and highly scalable.

What are Websockets?

Websockets are a protocol for bidirectional communication between clients and servers. They provide a persistent connection that allows real-time data transfer. Unlike HTTP, which is a request-response protocol, websockets allow the server to push data to the client without the need for the client to request it.

How to Use Websockets with K6

To use websockets with K6, you need to install the k6-ws extension. This extension provides a WebSocket class that you can use to create WebSocket connections in your test scripts.

Installing the k6-ws Extension

You can install the k6-ws extension using npm:

npm install k6-ws

Creating a WebSocket Connection

To create a WebSocket connection, you need to use the WebSocket class provided by the k6-ws extension. Here’s an example:

import { WebSocket } from 'k6/ws';export default function () {const url = 'wss://echo.websocket.org';const params = { tags: { my_tag: 'hello' } };const socket = new WebSocket(url, null, params);
socket.on('open', () => {console.log('WebSocket opened');socket.send('Hello, server!');});
socket.on('message', (message) => {console.log(`WebSocket message received: ${message}`);socket.close();});
socket.on('close', () => {console.log('WebSocket closed');});}

In this example, we are creating a WebSocket connection to the echo.websocket.org server. We are also passing some parameters to the WebSocket constructor, such as tags, which can be used to tag the metrics generated by the connection.

Once the connection is open, we send a message to the server and listen for messages. When a message is received, we log it to the console and close the connection.

Load Testing with Websockets

Load testing with websockets is similar to load testing with HTTP requests. You need to create a scenario that simulates user behavior and executes it using K6.

Here’s an example scenario that uses websockets:

import { check } from 'k6';import { WebSocket } from 'k6/ws';export default function () {const url = 'wss://echo.websocket.org';const socket = new WebSocket(url);
socket.on('open', () => {console.log('WebSocket opened');socket.send('Hello, server!');});
const res = socket.recv();check(res, { 'message received': (r) => r === 'Hello, server!' });
socket.close();
console.log('WebSocket closed');}

In this scenario, we create a WebSocket connection and send a message to the server. We then wait for a response and check that the response is what we expect. Finally, we close the connection.

WebSocket Options

The WebSocket class provided by the k6-ws extension accepts the following options:

params: An object containing parameters to pass to the WebSocket constructor.
responseTimeout: The amount of time to wait for a response from the server (in seconds).
pings: An array of ping messages to send to the server.
pongHandler: A function that will be called when a pong message is received from the server.

Conclusion

Websockets are a powerful tool for building real-time applications. With K6, you can also use websockets for load testing. By following the steps outlined in this article, you can easily create websocket connections in your K6 tests and simulate real-world user behavior.