Browser Performance Testing

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.

Overview

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.

Going a step further, GitLab can show the Performance report right in the merge request widget area (see below).

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 in your .gitlab-ci.yml file that generates the Performance report artifact. For more information on how the Performance job should look like, check the example on Configuring Browser Performance Testing.

GitLab then checks this report, compares key performance metrics for each page between the source and target branches, and shows the information right on the merge request.

Note: 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

Configuring Browser Performance Testing

This example shows how to run the sitespeed.io container on your code by using GitLab CI/CD and sitespeed.io using Docker-in-Docker.

First, you need GitLab Runner with docker-in-docker build.

Once you set up the Runner, add a new job to .gitlab-ci.yml that generates the expected report.

For GitLab 12.4 and later, to define the performance job, you must include the Browser-Performance.gitlab-ci.yml template that’s provided as a part of your GitLab installation. For GitLab versions earlier than 12.4, you can copy and use the job as defined in that template.

Caution: The job definition provided by the template does not support Kubernetes yet. For a complete example of a more complex setup that works in Kubernetes, see here.

Add the following to your .gitlab-ci.yml file:

include:
  template: Verify/Browser-Performance.gitlab-ci.yml

performance:
  variables:
    URL: https://example.com
Caution: The job definition provided by the template is supported in GitLab 11.5 and later versions. It also requires GitLab Runner 11.5 or later. For earlier versions, use the previous job definitions.

The above example will create a performance job in your CI/CD pipeline and will run sitespeed.io against the webpage you defined in URL to gather key metrics. The GitLab plugin for sitespeed.io is downloaded in order to save the report as a Performance report artifact that you can later download and analyze. Due to implementation limitations we always take the latest Performance artifact available.

The full HTML sitespeed.io report will also be saved as an artifact, and if you have GitLab Pages enabled, it can be viewed directly in your browser.

It is also possible to customize options by setting the SITESPEED_OPTIONS variable. For example, this is how to override the number of runs sitespeed.io will make on the given URL:

include:
  template: Verify/Browser-Performance.gitlab-ci.yml

performance:
  variables:
    URL: https://example.com
    SITESPEED_OPTIONS: -n 5

For further customization options for sitespeed.io, including the ability to provide a list of URLs to test, please see the Sitespeed.io Configuration documentation.

Tip: Key metrics are automatically extracted and shown in the merge request widget.

Performance testing on Review Apps

The above CI YML is great for testing against static environments, and it can be extended for dynamic environments. There are a few extra steps to take to set this up:

  1. The performance job should run after the dynamic environment has started.
  2. In the review job, persist the hostname and upload it as an artifact so it’s available to the performance job (the same can be done for static environments like staging and production to unify the code path). Saving it as an artifact is as simple as echo $CI_ENVIRONMENT_URL > environment_url.txt in your job’s script.
  3. In the performance job, read the previous artifact into an environment variable, in this case $URL because this is what our sitespeed.io command uses for the URL parameter. Because Review App URLs are dynamic, we define the URL variable through before_script instead of variables.
  4. You can now run the sitespeed.io container against the desired hostname and paths.

Your .gitlab-ci.yml file would look like:

stages:
  - deploy
  - performance

include:
  template: Verify/Browser-Performance.gitlab-ci.yml

review:
  stage: deploy
  environment:
    name: review/$CI_COMMIT_REF_SLUG
    url: http://$CI_COMMIT_REF_SLUG.$APPS_DOMAIN
  script:
    - run_deploy_script
    - echo $CI_ENVIRONMENT_URL > environment_url.txt
  artifacts:
    paths:
      - environment_url.txt
  only:
    - branches
  except:
    - master

performance:
  dependencies:
    - review
  before_script:
    - export URL=$(cat environment_url.txt)

Previous job definitions

Caution: Before GitLab 11.5, Performance job and artifact had to be named specifically to automatically extract report data and show it in the merge request widget. While these old job definitions are still maintained they have been deprecated and may be removed in next major release, GitLab 12.0. You are advised to update your current .gitlab-ci.yml configuration to reflect that change.

For GitLab 11.4 and earlier, the job should look like:

performance:
  stage: performance
  image: docker:git
  variables:
    URL: https://example.com
  services:
    - docker:stable-dind
  script:
    - mkdir gitlab-exporter
    - wget -O ./gitlab-exporter/index.js https://gitlab.com/gitlab-org/gl-performance/raw/master/index.js
    - mkdir sitespeed-results
    - docker run --shm-size=1g --rm -v "$(pwd)":/sitespeed.io sitespeedio/sitespeed.io:6.3.1 --plugins.add ./gitlab-exporter --outputFolder sitespeed-results $URL
    - mv sitespeed-results/data/performance.json performance.json
  artifacts:
    paths:
      - performance.json
      - sitespeed-results/