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Browser Performance Testing

Introduced in GitLab Premium 10.3.

Overview

If your application offers a web interface and you are using GitLab CI/CD, you can quickly determine the performance impact of pending code changes.

GitLab uses Sitespeed.io, a free and open source tool for measuring the performance of web sites, and has built a simple Sitespeed plugin which outputs the results in a file called performance.json. This plugin outputs the performance score for each page that is analyzed.

The Sitespeed.io performance score is a composite value based on best practices, and we will be expanding support for additional metrics in a future release.

Use cases

For instance, consider the following workflow:

  1. A member of the marketing team is attempting to track engagement by adding a new tool
  2. With browser performance metrics, they see how their changes are impacting the usability of the page for end users
  3. The metrics show that after their changes the performance score of the page has gone down
  4. When looking at the detailed report, they see that the new Javascript library was included in <head> which affects loading page speed
  5. They ask a front end developer to help them, who sets the library to load asynchronously
  6. The frontend developer approves the merge request and authorizes its deployment to production

How it works

First of all, you need to define a job named performance in your .gitlab-ci.yml file. Check how the performance job should look like.

GitLab runs the Sitespeed.io container and compares key performance metrics for each page between the source and target branches of a merge request. The difference for each page is then shown right on the merge request.

In order for the report to show in the merge request, there are two prerequisites:

  • the specified job must be named performance
  • the resulting report must be named performance.json and uploaded as an artifact

If the performance report doesn't have anything to compare to, no information will be displayed in the merge request area. That is the case when you add the performance job in your .gitlab-ci.yml for the very first time. Consecutive merge requests will have something to compare to and the performance report will be shown properly.

Performance Widget