In today’s article, I guide you through your Azure DevOps setup to perform automated load tests using k6. Before we begin, I want to take a minute to explain what load tests are and why they are essential.

What is a load test?

There are many different types of testing in software development. For example, some tests check that different models of an application work together as expected (integration testing), some focus on the business requirements of an application by verifying the output of action without considering the intermediate state (functional testing), and others perform different types of testing. Load testing is a type of performance testing as well as a type of stress test and capacity test. It focuses on verifying the application’s stability and reliability under both normal and peak load conditions.

Important: While load testing tests your application under realistic average or peak loads, stress testing tests it under conditions that far exceed realistic estimates.

How does load testing work?

During load testing, the testing tool simulates the concurrent requests to your application through multiple virtual users (VUs) and measures insights like response times, throughput rates, resource utilization levels, and more.

Why is it important?

In today’s world, both enterprises and consumers rely on digital applications for crucial functions. For this reason, even a small failure can be costly both in terms of reputation and money. For example, imagine if Amazon did not know the amount of traffic that its servers could sustain; it would fail to supply requests from its customer during peak seasons like Black Friday. You might think that this event is unlikely. However, according to a survey taken by the global research and advisory firm Gartner, in 2020, 25% of respondents reported the average hourly downtime cost of their application was between $301,000 and $400,000. Furthermore, 17% said it cost them $5M per hour.

What is k6?

k6 is an open-source load testing tool written in Go that embeds a JavaScript runtime to allow developers to write performance tests in JavaScript. Each script must have at least one default function. This function represents the entry point of the virtual user. The structure of each script has two main areas:

• Init Code: Code outside the default function that is run only once per VU
• VU Code: Code inside the default function that runs continuously as long as the test is running

// init code
export default function() {
  // vu code
}

If you want to define characteristics like duration or DNS, or if you want to increase or decrease the number of VU during the test, you can use the options objects as follows:

export let options = {
   test_1: {
      executor: 'constant-arrival-rate',
      rate: 90,
      timeUnit: '1m',
      duration: '5m',
      preAllocatedVUs: 10, 
      tags: { test_type: 'api' },
      env: { API_PROTOCOL: 'http' },
      exec: 'api',
    },
    test_2: {
      executor: 'ramping-arrival-rate',
      stages: [
        { duration: '30s', target: 600 }, 
        { duration: '6m30s', target: 200 },
        { duration: '90s', target: 15 }, 
      ],
      startTime: '90s', 
      startRate: 15,
      timeUnit: '10s',      
      preAllocatedVUs: 50,
      maxVUs: 1000, 
      tags: { test_type: 'api' },
      env: { API_PROTOCOL: 'https' }, 
      exec: 'api',
    },
};

Azure DevOps and k6

Processes like continuous integration promote shift-left testing, giving you the advantage of discovering and addressing issues in the early stages of application development. However, you should run load tests designed to determine if your application can handle requests in an environment as close as possible to production. While the cost of maintaining an environment identical to that of production may be prohibitive, you should make it as similar as possible. If you have the resources, a solution might be to create a staging environment that is a copy of our production environment. Otherwise, you can consider carefully running tests on your production environment. In this demo, I will show you how to set up your DevOps to perform load testing of a .NET 5 API written in C## using k6. Now that you have a general understanding of this article’s leading players, let us dig into the demonstration.

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