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Experiment Guide

Experiments can be conducted by any GitLab team, most often the teams from the Growth Sub-department. Experiments are not tied to releases because they primarily target GitLab.com.

Experiments are run as an A/B/n test, and are behind an experiment feature flag to turn the test on or off. Based on the data the experiment generates, the team decides if the experiment had a positive impact and should be made the new default, or rolled back.

Experiment rollout issue

Each experiment should have an experiment rollout issue to track the experiment from rollout through to cleanup and removal. The rollout issue is similar to a feature flag rollout issue, and is also used to track the status of an experiment. When an experiment is deployed, the due date of the issue should be set (this depends on the experiment but can be up to a few weeks in the future). After the deadline, the issue needs to be resolved and either:

  • It was successful and the experiment becomes the new default.
  • It was not successful and all code related to the experiment is removed.

In either case, an outcome of the experiment should be posted to the issue with the reasoning for the decision.

Code reviews

Experiments' code quality can fail our standards for several reasons. These reasons can include not being added to the codebase for a long time, or because of fast iteration to retrieve data. However, having the experiment run (or not run) shouldn't impact GitLab availability. To avoid or identify issues, experiments are initially deployed to a small number of users. Regardless, experiments still need tests.

Experiments must have corresponding frontend or feature tests to ensure they exist in the application. These tests should help prevent the experiment code from being removed before the experiment cleanup process starts.

If, as a reviewer or maintainer, you find code that would usually fail review but is acceptable for now, mention your concerns with a note that there's no need to change the code. The author can then add a comment to this piece of code and link to the issue that resolves the experiment. The author or reviewer can add a link to this concern in the experiment rollout issue under the Experiment Successful Cleanup Concerns section of the description. If the experiment is successful and becomes part of the product, any items that appear under this section will be addressed.

Implementing an experiment

GLEX - or Gitlab::Experiment, the gitlab-experiment gem - is the preferred option for implementing an experiment in GitLab.

For more information, see Implementing an A/B/n experiment using GLEX.

This uses experiment feature flags.

Add new icons and illustrations for experiments

Some experiments may require you to add custom icons or illustrations to our codebase. This process is lengthy and at this stage, the outcome of the experiment uncertain. Therefore, you should postpone this effort until the experiment cleanup process.

We recommend the following workflow:

  1. Review the Pajamas guidelines for icons and illustrations.
  2. Add an icon or illustration as an .svg file in the /app/assets/images (or EE) path in the GitLab repository.
  3. Use image_tag or image_path to render it via the asset pipeline.
  4. If the experiment is a success, designers add the new icon or illustration to the Pajamas UI kit as part of the cleanup process. Engineers can then add it to the SVG library and modify the implementation based on the Frontend Development Guidelines.

Turn off all experiments

When there is a case on GitLab.com (SaaS) that necessitates turning off all experiments, we have this control.

You can toggle experiments on SaaS on and off using the gitlab_experiment feature flag.

This can be done via chatops:

  • disable: /chatops run feature set gitlab_experiment false
  • enable: /chatops run feature delete gitlab_experiment