Simulating heavy traffic

Gatling and Gatling Enterprise are load testing solutions designed for web applications. You can simulate up to millions of virtual users navigating on your application. Load testing helps to discover bottlenecks, points of weakness, slowdowns and crashes of applications under heavy traffic.

Why load testing is critical for your business to handle heavy traffic

Traffic spikes often happen in critical situations for your business. Go-lives of your applications, seasonal events, national TV appearances, or ticket sales opening can bring a lot of unexpected but wanted visitors.

By simulating peaks of traffic in complex user scenarios, you can analyze your application’s performance precisely and identify its bottlenecks.

It can be a feature, a microservice, your infrastructure or even your architecture, load testing is here to help you find the culprit and adjust your resources accordingly.

Load testing can have a huge impact on your business. Cost, image, user experience, performance and even turnover… Your website is your face to the world and it sends signals to your customers.

Why load testing matters for your business

What are the factors that will influence the performance of your website?

When you browse a website, it is essential that the performance in terms of how it  loads and displays on a screen is fast enough that it doesn’t diminish the user experience. This performance can be measured using the response time to load the different contents of your web page.

We can distinguish two types of performance:

  • One that is visible to the user: The front-end’s performance will be measured by the time it takes the browser to load and display the elements of the web page. Depending on the elements and animations present on the site, the response time can be longer or shorter.
  • One that is invisible to the user: The back-end, which mainly concerns the response time of the server (calculation time) and in the case of an overload of the server some requests can timeout or go up as an error.

These two aspects will impact the performance of your website in different ways. It is important to act on the front-end as well as on the back-end.

The response time of the front-end depends mostly on the performance of the visitor’s browser. The website will load using the memory of the web browser: if the user has a low performance computer, then the website will basically take much longer to be displayed than with a modern and powerful computer. For this matter, you can adapt the scripts, the sizes of the images embedded on your site.

On the other hand, the response time of the back-end is very much related to the performance of the server on which your website is hosted. Indeed, if your web server is poorly dimensioned and can’t keep up with the load and the increase in the number of visitors, then the performance for the user will be degraded and will strongly impact the user experience. If you are new to this area, keep in mind that there are 5 steps to help build your load testing strategy.

When should you load test your website or application?

In summary, you should think about load testing your website or your application when you want to optimize its availability and at each key moment of its evolution.

It may be appropriate to perform a load test each time you update your website or your application to ensure that this update does not degrade performance.

The frequency of the tests will also depend on the evolution of the number of users. Think of monitoring the number of active users simultaneously on your website in order to define relevant parameters for your tests.

If your traffic remains constant every month, it may be interesting to consider load testing your website every month and compare with the performance of the past month.

Be aware, if your application or your website is subject to strong traffic surges, you will have to perform load tests more regularly and consider resizing your back-end (your servers) according to the load peaks observed.

Load testing Cycle

How does load testing work?

There are numerous tests you can do to check your website’s health. Load tests are focused around heavy traffic simulation.

A “load generator” will create virtual users by sending requests (HTTP or any other web protocol) to a server . These requests are generated according to a workflow defined in a simulation to reproduce a real user’s behavior. Thus, the number of requests will define the number of users you want to see.

Since virtual users are made of requests, Gatling and Gatling Enterprise are agnostic solutions. It means that you can test all your applications, whatever the underlying technologies, as long as they are based on web protocols.

Then, the load generator collects the response times of all the requests. If you are using Gatling, it will generates an HTML report, including data and charts about your test.
If you are using Gatling Enterprise, your load generators send all the metrics collected to a database. You can then watch your reports in real time in a centralized web interface and compare your test’s results with the history of all your load tests.

How to use Gatling and Gatling Enterprise?

Load testing is about experimenting and investigating for heavy traffic issues. You need first to have a good knowledge of your users’ behaviors, to craft your simulations. Gatling’s recorder allows users to bootstrap simulation’s code and then test their application or only parts of it, to understand where are the bottlenecks.

You can use various injection profiles (how your virtual users are injected in your system) and different kinds of load tests to investigate your application:

  • Capacity test: increase step by step your users’ arrival rate until your system crashes, to find out how many concurrent users your system can handle
  • Stress test: simulate a peak of traffic with a high number of virtual users arriving in your system within the same time window, to validate your application’s performances according to your business strategy
  • Soak test: run a load test over several hours or days to measure the long-term impacts of traffic on your website (e.g. memory leaks)

At the end of your tests, you can analyze your reports and iterate by changing one or several parameters, to investigate further your performance issues and ultimately solve them.

Open source or for business, Gatling provides a solution adapted to each type of project. It’s also compatible with numerous third parties and technical environments. In the end, it is built to be easy to use and flexible. That’s why it’s used by a big community all over the world. A community you can always poke for help.