Using Git submodules with GitLab CI

Notes:

• GitLab 8.12 introduced a new CI job permissions model and you are encouraged to upgrade your GitLab instance if you haven't done already. If you are not using GitLab 8.12 or higher, you would need to work your way around submodules in order to access the sources of e.g., gitlab.com/group/project with the use of SSH keys.
• With GitLab 8.12 onward, your permissions are used to evaluate what a CI job can access. More information about how this system works can be found in the Jobs permissions model.
• The HTTP(S) Git protocol must be enabled in your GitLab instance.

Configuring the .gitmodules file

If dealing with Git submodules, your project will probably have a file named .gitmodules.

Let's consider the following example:

1. Your project is located at https://gitlab.com/secret-group/my-project.
2. To checkout your sources you usually use an SSH address like git@gitlab.com:secret-group/my-project.git.
3. Your project depends on https://gitlab.com/group/project, which you want to include as a submodule.

If you are using GitLab 8.12+ and your submodule is on the same GitLab server, you must update your .gitmodules file to use relative URLs. Since Git allows the usage of relative URLs for your .gitmodules configuration, this easily allows you to use HTTP(S) for cloning all your CI jobs and SSH for all your local checkouts. The .gitmodules would look like:

[submodule "project"]
  path = project
  url = ../../group/project.git

The above configuration will instruct Git to automatically deduce the URL that should be used when cloning sources. Whether you use HTTP(S) or SSH, Git will use that same channel and it will allow to make all your CI jobs use HTTP(S) (because GitLab CI only uses HTTP(S) for cloning your sources), and all your local clones will continue using SSH.

For all other submodules not located on the same GitLab server, use the full HTTP(S) protocol URL:

[submodule "project-x"]
  path = project-x
  url = https://gitserver.com/group/project-x.git

Once .gitmodules is correctly configured, you can move on to configuring your .gitlab-ci.yml.

Using Git submodules in your CI jobs

There are a few steps you need to take in order to make submodules work correctly with your CI jobs:

1. First, make sure you have used relative URLs for the submodules located in the same GitLab server.

2. Next, if you are using gitlab-ci-multi-runner v1.10+, you can set the GIT_SUBMODULE_STRATEGY variable to either normal or recursive to tell the runner to fetch your submodules before the job:

   variables:
     GIT_SUBMODULE_STRATEGY: recursive

   See the .gitlab-ci.yml reference for more details about GIT_SUBMODULE_STRATEGY.

3. If you are using an older version of gitlab-ci-multi-runner, then use git submodule sync/update in before_script:

   before_script:
     - git submodule sync --recursive
     - git submodule update --init --recursive

   --recursive should be used in either both or none (sync/update) depending on whether you have recursive submodules.

The rationale to set the sync and update in before_script is because of the way Git submodules work. On a fresh Runner workspace, Git will set the submodule URL including the token in .git/config (or .git/modules/<submodule>/config) based on .gitmodules and the current remote URL. On subsequent jobs on the same Runner, .git/config is cached and already contains a full URL for the submodule, corresponding to the previous job, and to a token from a previous job. sync allows to force updating the full URL.