Review Apps

Review Apps are a collaboration tool that takes the hard work out of providing an environment to showcase product changes.


Review Apps:

  • Provide an automatic live preview of changes made in a feature branch by spinning up a dynamic environment for your merge requests.
  • Allow designers and product managers to see your changes without needing to check out your branch and run your changes in a sandbox environment.
  • Are fully integrated with the GitLab DevOps LifeCycle.
  • Allow you to deploy your changes wherever you want.

Review Apps Workflow

In the above example:

  • A Review App is built every time a commit is pushed totopic branch.
  • The reviewer fails two reviews before passing the third review.
  • Once the review as passed, topic branch is merged into master where it's deploy to staging.
  • After been approved in staging, the changes that were merged into master are deployed in to production.

How Review Apps work

A Review App is a mapping of a branch with an environment. Access to the Review App is made available as a link on the merge request relevant to the branch.

The following is an example of a merge request with an environment set dynamically.

Review App in merge request

In this example, a branch was:

  • Successfully built.
  • Deployed under a dynamic environment that can be reached by clicking on the View app button.

Configuring Review Apps

Review Apps are built on dynamic environments, which allow you to dynamically create a new environment for each branch.

The process of configuring Review Apps is as follows:

  1. Set up the infrastructure to host and deploy the Review Apps.
  2. Install and configure a Runner to do deployment.
  3. Set up a job in .gitlab-ci.yml that uses the predefined CI environment variable ${CI_COMMIT_REF_NAME} to create dynamic environments and restrict it to run only on branches.
  4. Optionally, set a job that manually stops the Review Apps.


The following are example projects that demonstrate Review App configuration:

See also the video Demo: Cloud Native Development with GitLab, which includes a Review Apps example.

Route Maps

Introduced in GitLab 8.17. In GitLab 11.5, the file links are available in the merge request widget.

Route Maps allows you to go directly from source files to public pages on the environment defined for Review Apps.

Once set up, the review app link in the merge request widget can take you directly to the pages changed, making it easier and faster to preview proposed modifications.

Configuring Route Maps involves telling GitLab how the paths of files in your repository map to paths of pages on your website using a Route Map. Once set, GitLab will display View on ... buttons, which will take you to the pages changed directly from merge requests.

To set up a route map, add a a file inside the repository at .gitlab/route-map.yml, which contains a YAML array that maps source paths (in the repository) to public paths (on the website).

Route Maps example

The following is an example of a route map for Middleman, a static site generator (SSG) used to build GitLab's website, deployed from its project on

# Team data
- source: 'data/team.yml' # data/team.yml
  public: 'team/' # team/

# Blogposts
- source: /source\/posts\/([0-9]{4})-([0-9]{2})-([0-9]{2})-(.+?)\..*/ # source/posts/
  public: '\1/\2/\3/\4/' # 2017/01/30/around-the-world-in-6-releases/

# HTML files
- source: /source\/(.+?\.html).*/ # source/index.html.haml
  public: '\1' # index.html

# Other files
- source: /source\/(.*)/ # source/images/blogimages/around-the-world-in-6-releases-cover.png
  public: '\1' # images/blogimages/around-the-world-in-6-releases-cover.png

Mappings are defined as entries in the root YAML array, and are identified by a - prefix. Within an entry, there is a hash map with two keys:

  • source
    • A string, starting and ending with ', for an exact match.
    • A regular expression, starting and ending with /, for a pattern match:
      • The regular expression needs to match the entire source path - ^ and $ anchors are implied.
      • Can include capture groups denoted by () that can be referred to in the public path.
      • Slashes (/) can, but don't have to, be escaped as \/.
      • Literal periods (.) should be escaped as \..
  • public, a string starting and ending with '.
    • Can include \N expressions to refer to capture groups in the source regular expression in order of their occurrence, starting with \1.

The public path for a source path is determined by finding the first source expression that matches it, and returning the corresponding public path, replacing the \N expressions with the values of the () capture groups if appropriate.

In the example above, the fact that mappings are evaluated in order of their definition is used to ensure that source/index.html.haml will match /source\/(.+?\.html).*/ instead of /source\/(.*)/, and will result in a public path of index.html, instead of index.html.haml.

Once you have the route mapping set up, it will take effect in the following locations:

  • In the merge request widget. The:

    • View app button will take you to the environment URL set in .gitlab-ci.yml.

    • Dropdown will list the first 5 matched items from the route map, but you can filter them if more than 5 are available.

      View app file list in merge request widget

  • In the diff for a merge request, comparison, or commit.

    "View on env" button in merge request diff

  • In the blob file view.

    "View on env" button in file view

Working with Review Apps

After adding Review Apps to your workflow, you follow the branched Git flow. That is:

  1. Push a branch and let the Runner deploy the Review App based on the script definition of the dynamic environment job.
  2. Wait for the Runner to build and deploy your web application.
  3. Click on the link that provided in the merge request related to the branch to see the changes live.


Review App limitations are the same as environments limitations.