Caching Bundler on GitHub Actions

When GitHub actions first launched, the recommended way to cache your Bundler dependencies was to use GitHub’s cache action. However, that is no longer the case. You should be using the Ruby team’s setup-ruby action instead.

I’m not quite sure when this changed. Here’s how you used to cache Bundler using GitHub’s cache action.

# workflow.yml

- name: cache gems
  uses: actions/cache@v2
  with:
    path: vendor/bundle
    key: ${{ runner.os }}-gem-bundler-${{ hashFiles('**/Gemfile.lock') }}
    restore-keys: |
      ${{ runner.os }}-gem-bundler-

Apparently, caching gems with Bundler is not trivial and actually quite difficult to get correct. I don’t know the details, but I do know that my GitHub workflows started failing in strange ways when attempting to use actions/cache. When updating gems and especially when updating Bundler to a new version, the caching would fail on GitHub’s CI machines, which resulted in bundle exec failing because no gems could be found.

Migrating the above workflow step to use Ruby’s setup-ruby action is easy.

# workflow.yml

- name: ruby setup
  uses: ruby/setup-ruby@v1
  with:
    ruby-version: 2.7
    bundler-cache: true

Not only is it simpler, but it works! I have been using this for a few months now it I have not had any issues. If you have old workflows that still use actions/cache, you should update them to use ruby/setup-ruby instead.