Browser Performance Testing

If your application offers a web interface and you’re 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. GitLab has built a simple Sitespeed plugin which outputs the performance score for each page analyzed in a file called performance.json. The Sitespeed.io performance score is a composite value based on best practices.

GitLab can show the Performance report in the merge request widget area.

Use cases

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 the new JavaScript library was included in <head>, which affects loading page speed.
  5. They ask for help from a front end developer, who sets the library to load asynchronously.
  6. The frontend developer approves the merge request, and authorizes its deployment to production.

How browser performance testing works

First, define a job in your .gitlab-ci.yml file that generates the Performance report artifact. GitLab then checks this report, compares key performance metrics for each page between the source and target branches, and shows the information in the merge request.

For an example Performance job, see Configuring Browser Performance Testing.

Note: If the Performance report has no data to compare, such as when you add the Performance job in your .gitlab-ci.yml for the very first time, no information displays in the merge request widget area. Consecutive merge requests will have data for comparison, 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.

  1. First, set up GitLab Runner with a Docker-in-Docker build.
  2. After configuring the Runner, add a new job to .gitlab-ci.yml that generates the expected report.
  3. Define the performance job according to your version of GitLab:

    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 Browser-Performance-Testing.gitlab-ci.yml.
  4. 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 creates a performance job in your CI/CD pipeline and runs sitespeed.io against the webpage you defined in URL to gather key metrics. The GitLab plugin for sitespeed.io is downloaded 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 is saved as an artifact, and if GitLab Pages is enabled, it can be viewed directly in your browser.

You can also customize options by setting the SITESPEED_OPTIONS variable. For example, you can override the number of runs sitespeed.io makes 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.

Configuring degradation threshold

Introduced in GitLab 13.0.

You can configure the sensitivity of degradation alerts to avoid getting alerts for minor drops in metrics. This is done by setting the DEGRADATION_THRESHOLD variable. In the example below, the alert will only show up if the Total Score metric degrades by 5 points or more:

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

performance:
  variables:
    URL: https://example.com
    DEGRADATION_THRESHOLD: 5

The Total Score metric is based on sitespeed.io’s coach performance score. There is more information in the coach documentation.

Performance testing on Review Apps

The above CI YAML configuration is great for testing against static environments, and it can be extended for dynamic environments, but a few extra steps are required:

  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. You can save it as an artifact with 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, use $URL because the sitespeed.io command uses it for the URL parameter. Because Review App URLs are dynamic, 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, the 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. GitLab recommends you 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/