Site Reliability Engineering

What is K6 & How to get started with k6

k6 is an open source tool and cloud service that makes load testing easy for developers and QA engineers

Giulia Di Pietro

Jun 02, 2022

In my previous blog post, I talked about performance engineering and mentioned various tools you can use for performance testing.

k6 is one of them: an open source tool developed by Grafana Labs. In this blog post, I’d like to share with you what k6 is, and what features it has and guide you through an example to get you started with k6.

Introduction to k6

k6 is a package that can be installed either in bare metal (Windows, Linux - debian or Fedora, and Macos), or in a docker environment with the help of the official docker image provided by the Grafana k6 team.

The k6 client command line allows you to generate many users directly from the client. This means that the k6 client acts as a controller (component orchestrating the test ) and a load generator (component sending the traffic to your application under test).

k6 doesn’t provide a UI or dashboard to analyze your data. That’s why there are many extensions to help you store the load test statistics onto external storage, like Prometheus, InfluxDB, etc.

But a SaaS solution for cloud (k6 cloud) provides a WebUI to help you design, schedule, and run tests using several load generators, which is a better fit for enterprise use.

The k6 solution supports out-of-the-box HTTP (1.1 and 2, grpc and WebSocket). Still, there are several extensions for MQTT, AMQP, Kafka, Mllp, Redis, generating stress on your database level and driving a headless browser.

How to build a test case in k6

Now, let’s move on to the practical part. Here’s how you can build a test case in k6.

A k6 test relies on a script defined in JavaScript using the k6 library. k6 doesn’t have a recorder, so you have to manually define the requests workflow that will help you reproduce real end-user traffic.

To start building your test case, you'll need to import the correct libraries:

For HTTP/HTTPS:

            import http from 'k6/http';

For grpc

            import grpc from 'k6/net/grpc';

For websocket

            import ws from 'k6/ws or websocket

Once the import is done, you will be able to create a request. In the case of http:

            http.get( )

            http.post(url, pauload, params./.etc)

The request can have several properties, i.e.:

1

Name the transaction
2

Change the expected response code
3

Tag your traffic to group request that are related (for example product/dedeed or product/5464563456 is at the end product/{product id})

If a transaction is a combination of several http requests you can group your request in a “transaction” with group:

            group('visit product listing page', function () {

 // ...

 });

When you run your k6 test, it is also important to validate that the application is generating the expected responses. The Check library helps you validate your responses:

            const res = http.get('http://test.k6.io/');

 check(res, {

 'is status 200': (r) => r.status === 200,

 });

When designing your load test scenario, it’s really important to properly correlate your test to make it realistic. That is why you would probably need to extract content from the response, like the product ID, to use it on the subsequent request. The correlation mechanism can be easily applied by regexp on the res.body content.

Test script structure

The test script of k6 is structured in the following way:

            // 1. init code
Options{
}
export function setup() {
 // 2. setup code
}
export default function (data) {
 // 3. VU code
}
export function teardown(data) {
 // 4. teardown code
}

The first section is the init, where we import the right libraries, and define global variables and settings of the test with the option object.

The setup (optional) is all the code that will run to set up the environment and build data used during the actual test. Default: the actual test that will iterate until the end of the test (defined in the options). Teardown (optional) runs at the test's end before the user ends.

To summarize, init will be executed once per virtual user, set up only once, the default will iterate the script for each vu during the entire test, and a teardown is executed once per script.

Options

The option object holds all the information related to your test:

1

How many users to simulate
2

How to ramp up
3

The duration of the test
4

How to ramp down

Thresholds

k6 allows you to define targets of tests by defining thresholds on statistics. For example:

            thresholds: {

 http_req_failed: ['rate<0.01'], // http errors should be less than 1%

 http_req_duration: ['p(95)<200'], // 95% of requests should be below 200ms

 },

Metrics

k6 allows you to create metrics to report at the end of your tests. There are several metric types: Gauge, Rate, Counter, Trends.

You need to define in the init the metric type that you would like to build and add value to the metric in the default script.

For example:

            const myGauge = new Gauge('my_gauge'); 

export default function () {

 myGauge.add(3);

 myGauge.add(1);

 myGauge.add(2);

}

k6 commands

To run a test, you need to use the command “k6 run” and the name of your script .

            k6 run test.js

k6 report and results

k6 will generate a summary report display in the output of the test. You can also specify if you want to generate a JSON file containing your test's data points ( with the option-out JSON file). You can also use an output extension to push the statistics to external storage.

k6 extensions

k6 comes with a large number of extensions, which you can find listed here: k6 Extensions

K6 is built as an xk6 tool that helps us build our k6 client by adding extensions.

To build the k6 client, we use the xk6 client :

            xk6 build [<k6_version>] [--out /k6] [--with <module[@version][=replacement]>...]

k6 also provides a fantastic extension called xk6-distributed tracing to create the first open telemetry spans.

If you're testing a solution producing OpenTelemty measurement, then this plugin will be extremely helpful.

There is also another extension related to Kubernetes that facilitate the creation of distributed test in our cluster, it’s the k6 operator.

The operator adds a new CRD in our Kubernetes cluster: K6

That will hold all the settings to run a test :

            apiVersion: k6.io/v1alpha1
kind: K6
metadata:
 name: k6-sample
spec:
 parallelism: 4
 script:
 configMap:
 name: k6-test
 file: test.js
 separate: false
 runner:
 image: <custom-image>
 metadata:
 labels:
 cool-label: foo
 annotations:
 cool-annotation: bar
 securityContext:
 runAsUser: 1000
 runAsGroup: 1000
 runAsNonRoot: true
 resources:
 limits:
 cpu: 200m
 memory: 1000mi
 requests:
 cpu: 100m
 memory: 500Mi
 starter:
 image: <custom-image>
 metadata:
 labels:
 cool-label: foo
 annotations:
 cool-annotation: bar
 securityContext:
 runAsUser: 2000
 runAsGroup: 2000
 runAsNonRoot: true