Gemfile guidelines

When adding a new entry to Gemfile, or upgrading an existing dependency pay attention to the following rules.

Bundler checksum verification

In GitLab 15.5 and later, gem checksums are checked before installation. This verification is still experimental so it is only active for CI.

If the downloaded gem’s checksum does not match the checksum record in Gemfile.checksum, you will see an error saying that Bundler cannot continue installing a gem because there is a potential security issue.

You will see this error as well if you updated, or added a new gem without updating Gemfile.checksum. To fix this error, update the Gemfile.checksum.

You can opt-in to this verification locally by setting the BUNDLER_CHECKSUM_VERIFICATION_OPT_IN environment variable:

bundle install

Updating the checksum file

This needs to be done for any new, or updated gems.

  1. When updating Gemfile.lock, make sure to also update Gemfile.checksum with:

    bundle exec bundler-checksum init
  2. Check and commit the changes for Gemfile.checksum.

No gems fetched from Git repositories

We do not allow gems that are fetched from Git repositories. All gems have to be available in the RubyGems index. We want to minimize external build dependencies and build times. It’s enforced by the RuboCop rule Cop/GemFetcher.

Review the new dependency for quality

We should not add 3rd-party dependencies to GitLab that would not pass our own quality standards. This means that new dependencies should, at a minimum, meet the following criteria:

  • They have an active developer community. At the minimum a maintainer should still be active to merge change requests in case of emergencies.
  • There are no issues open that we know may impact the availability or performance of GitLab.
  • The project is tested using some form of test automation. The test suite must be passing using the Ruby version currently used by GitLab.
  • If the project uses a C extension, consider requesting an additional review from a C or MRI domain expert. C extensions can greatly impact GitLab stability and performance.

Request an Appsec review

When adding a new gem to our Gemfile or even changing versions in Gemfile.lock it is strongly recommended that you request a Security review. New gems add an extra security risk for GitLab, and it is important to evaluate this risk before we ship this to production. Technically, just adding a new gem and pushing to a branch in our main gitlab project is a security risk as it will run in CI using your credentials. As such you should evaluate early on if you think this gem seems legitimate before you even install it.

Reviewers should also be aware of our related recommendations for reviewing community contributions and take care before running a pipeline for community contributions that contains changes to Gemfile or Gemfile.lock.

License compliance

Refer to licensing guidelines for ensuring license compliance.

GitLab-created gems

Sometimes we create libraries within our codebase that we want to extract, either because we want to use them in other applications ourselves, or because we think it would benefit the wider community. Extracting code to a gem also means that we can be sure that the gem does not contain any hidden dependencies on our application code.

In general, we want to think carefully before doing this as there are also disadvantages:

  1. Gems - even those maintained by GitLab - do not necessarily go through the same code review process as the main Rails application.
  2. Extracting the code into a separate project means that we need a minimum of two merge requests to change functionality: one in the gem to make the functional change, and one in the Rails app to bump the version.
  3. Our needs for our own usage of the gem may not align with the wider community’s needs. In general, if we are not using the latest version of our own gem, that might be a warning sign.

In the case where we do want to extract some library code we’ve written to a gem, go through these steps:

  1. Start with the code in the Rails application. Here it’s fine to have the code in lib/ and loaded automatically. We can skip this step if the step below makes more sense initially.
  2. Before extracting to its own project, move the gem to vendor/gems and load it in the Gemfile using the path option. This gives us a gem that can be published to, with its own test suite and isolated set of dependencies, that is still in our main code tree and goes through the standard code review process.
  3. Once the gem is stable - we have been using it in production for a while with few, if any, changes - extract to its own project under the gitlab-org/ruby/gems namespace.

    • To create this project:
      1. Follow the instructions for new projects.
      2. Follow the instructions for setting up a CI/CD configuration.
      3. Follow the instructions for publishing a project.
    • See issue #325463 for an example.
    • In some cases we may want to move a gem to its own namespace. Some examples might be that it will naturally have more than one project (say, something that has plugins as separate libraries), or that we expect non-GitLab-team-members to be maintainers on this project as well as GitLab team members.

      The latter situation (maintainers from outside GitLab) could also apply if someone who currently works at GitLab wants to maintain the gem beyond their time working at GitLab.

When publishing a gem to, also note the section on gem owners in the handbook.

Upgrade Rails

When upgrading the Rails gem and its dependencies, you also should update the following:

You should also update npm packages that follow the current version of Rails:

  • @rails/ujs
    • Run yarn patch-package @rails/ujs after updating this to ensure our local patch file version matches.
  • @rails/actioncable

Upgrading dependencies because of vulnerabilities

When upgrading dependencies because of a vulnerability, we should pin the minimal version of the gem in which the vulnerability was fixed in our Gemfile to avoid accidentally downgrading.

For example, consider that the gem license_finder has thor as its dependency. thor was found vulnerable until its version 1.1.1, which includes the vulnerability fix.

In the Gemfile, make sure to pin thor to 1.1.1. The direct dependency license_finder should already have the version specified.

gem 'license_finder', '~> 6.0'
# Dependency of license_finder with fix for vulnerability
# _link to initial security issue that will become public in time_
gem 'thor', '>= 1.1.1'

Here we’re using the operator >= (greater than or equal to) rather than ~> (pessimistic operator) making it possible to upgrade license_finder or any other gem to a version that depends on thor 1.2.

Similarly, if license_finder had a vulnerability fixed in 6.0.1, we should add:

gem 'license_finder', '~> 6.0', '>= 6.0.1'

This way, other dependencies rather than license_finder can still depend on a newer version of thor, such as 6.0.2, but would not be able to depend on the vulnerable version 6.0.0.

A downgrade like that could happen if we introduced a new dependency that also relied on thor but had its version pinned to a vulnerable one. These changes are easy to miss in the Gemfile.lock. Pinning the version would result in a conflict that would need to be solved.

To avoid upgrading indirect dependencies, we can use bundle update --conservative.

When submitting a merge request including a dependency update, include a link to the Gem diff between the 2 versions in the merge request description. You can find this link on, select Review Changes to generate a comparison between the versions on For example, this is the gem diff for thor 1.0.0 vs 1.0.1. Use the links directly generated from RubyGems, since the links from GitLab or other code-hosting platforms might not reflect the code that’s actually published.