Rails upgrade guidelines

We strive to run GitLab using the latest Rails releases to benefit from performance, security updates, and new features.

Rails upgrade approach

Prepare an MR for GitLab.
Create patch releases and backports for security patches.

Prepare an MR for GitLab

Check the Upgrading Ruby on Rails guide and prepare the application for the upcoming changes.
Update the rails gem version in Gemfile.
Run bundle update --conservative rails.
For major and minor version updates, run bin/rails app:update and check if any of the suggested changes should be applied.
Update the activesupport version in qa/Gemfile.
Run bundle update --conservative activesupport in the qa folder.
Update the activerecord_version version in vendor/gems/attr_encrypted/attr_encrypted.gemspec.
Run bundle update --conservative activerecord in the vendor/gems/attr_encrypted folder.
Resolve any Bundler conflicts.
Ensure that @rails/ujs and @rails/actioncable npm packages match the new rails version in package.json.
Run yarn patch-package @rails/ujs after updating this to ensure our local patch file version matches.
Create an MR with the pipeline:run-all-rspec label and see if pipeline breaks.
To resolve and debug spec failures use git bisect against the rails repository. See the debugging section below.
Include links to the Gem diffs between the two versions in the merge request description. For example, this is the gem diff for activesupport 6.1.3.2 to 6.1.4.1.

Prepare an MR for Gitaly

No longer necessary as Gitaly no longer has Ruby code.

Create patch releases and backports for security patches

If the Rails upgrade was over a patch release and it contains important security fixes, make sure to release it in a GitLab patch release to self-managed customers. Consult with our release managers for how to proceed.

Deprecation Logger

We also log Ruby and Rails deprecation warnings into a dedicated log file, log/deprecation_json.log. It provides clues when there is code that is not adequately covered by tests and hence would slip past DeprecationToolkitEnv.

For GitLab SaaS, GitLab team members can inspect these log events in Kibana (https://log.gprd.gitlab.net/goto/f7cebf1ff05038d901ba2c45925c7e01).

Git bisect against Rails

Usually, if you know which Rails change caused the spec to fail, it adds additional context and helps to find the fix for the failure. To efficiently and quickly find which Rails change caused the spec failure you can use the git bisect command against the Rails repository:

Clone the rails project in a folder of your choice. For example, it might be the GDK root dir:
```
cd <GDK_FOLDER>
git clone https://github.com/rails/rails.git
```

Replace the gem 'rails' line in GitLab Gemfile with:

gem 'rails', ENV['RAILS_VERSION'], path: ENV['RAILS_FOLDER']

Set the RAILS_FOLDER environment variable with the folder you cloned Rails into:
```
export RAILS_FOLDER="<GDK_FOLDER>/rails"
```
Change the directory to RAILS_FOLDER and set the range for the git bisect command:
```
cd $RAILS_FOLDER
git bisect start <NEW_VERSION_TAG> <OLD_VERSION_TAG>
```
Where <NEW_VERSION_TAG> is the tag where the spec is red and <OLD_VERSION_TAG> is the one with the green spec. For example, git bisect start v6.1.4.1 v6.1.3.2 if we're upgrading from version 6.1.3.2 to 6.1.4.1. Replace <NEW_VERSION_TAG> with the tag where the spec is red and <OLD_VERSION_TAG> with the one with the green spec. For example, git bisect start v6.1.4.1 v6.1.3.2 if we're upgrading from version 6.1.3.2 to 6.1.4.1. In the output, you can see how many steps approximately it takes to find the commit.

Start the git bisect process and pass spec's filenames to scripts/rails-update-bisect as arguments. It can be faster to pick only one example instead of an entire spec file.

git bisect run <GDK_FOLDER>/gitlab/scripts/rails-update-bisect spec/models/ability_spec.rb
# OR
git bisect run <GDK_FOLDER>/gitlab/scripts/rails-update-bisect spec/models/ability_spec.rb:7

When the process is completed, git bisect prints the commit hash, which you can use to find the corresponding MR in the rails/rails repository.
Execute git bisect reset to exit the bisect mode.
Revert the changes to Gemfile:
```
git checkout -- Gemfile
```