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Last updated: 16 Jun 2021

Publish a Ruby gem

Naming

In general, the gem name should be the same as the thing you require when using it. This means using _, and not - to separate multi-word gem names. See the name your gem guide for more detailed guidance.

Also see the general policy on naming.

Versioning

Follow the guidelines on semver.org for assigning version numbers.

Versions should only be changed in a commit of their own, in a pull request of their own.

This alerts team members to the new version and allows for last-minute scrutiny before the new version is released. Also, by raising a separate pull request, we avoid version number conflicts between feature branches.

File layout

We should follow the scheme used by Bundler when creating gems (see this railscast).

Note

  • The version is stored in a file by itself in lib/<gem_name>/version.rb.
  • The Gemfile references the gemspec for gem dependencies. All gem dependencies should be specified in the gemspec.
  • The Gemfile.lock is never committed (it should be in the .gitignore file).

Releasing gem versions

The default Jenkins build script will automatically detect the presence of a gemspec file and publish the gem to rubygems.org. See the Jenkinsfile for govuk_app_config for an example.

Manually publishing gems from the CLI

Sometimes you may be required to publish a gem outside of Jenkins, if you need to release a patch or minor version below the current latest major version. For example, say you have a gem at version 1.0.0 and later release a major breaking change as version 2.0.0. If you still need to support apps using v1, and you want to apply a bugfix as a patch version 1.0.1, you would not be able to deploy off the main branch as this will include all of the breaking v2 changes.

To manually publish from the command line:

  1. Get your branch ready: checkout the tag of the previous major version (e.g. git checkout v1.0.0) and then create a branch pointing at this commit (git checkout -b bump-version-to-1.0.1).
  2. Get your code ready: make your code changes, including adding a CHANGELOG entry and bumping the version number.
  3. Commit.
  4. Manually follow the steps of the publishGem function in govuk-jenkinslib i.e. check your new version doesn’t already exist, build & publish the gem, make and push a git tag. The RubyGems credentials can be found in govuk-secrets.
  5. Tidy up: open a pull request for this branch against main. There will be merge conflicts, which you’ll have to manually resolve before you can merge. Do this without rebasing, as we want to keep the original main history. You’ll end up with a meta commit like Merge pull request #1 from username/branch-name, but the full history of both main and your branch will be intact.

Clearing the gemstash cache

When a new gem version is released, it may not be available immediately on Jenkins. This is due to gemstash, our gem mirror. It caches versions for up to 30 minutes. To force it to clear, restart gemstash on the apt machine in the relevant environment, e.g. for integration:

gds govuk c ssh -e integration apt 'sudo docker restart gemstash'

To clear the cache for the CI Jenkins instance, run this in integration.

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