Should Gemfile.lock be included in .gitignore?

Update for 2022 from TrinitronX

Fast-forward to 2021 and now Bundler docs [web archive] now say to commit the Gemfile.lock inside a gem... ¯_(ツ)_/¯ I guess it makes sense for developers and ease of use when starting on a project. However, now CI jobs need to be sure to remove any stray Gemfile.lock files to test against other versions.

Legacy answer ~2010

Assuming you're not writing a rubygem, Gemfile.lock should be in your repository. It's used as a snapshot of all your required gems and their dependencies. This way bundler doesn't have to recalculate all the gem dependencies each time you deploy, etc.

From cowboycoded's comment below:

If you are working on a gem, then DO NOT check in your Gemfile.lock. If you are working on a Rails app, then DO check in your Gemfile.lock.

Here's a nice article explaining what the lock file is.

The real problem happens when you are working on an open-source Rails app that needs to have a configurable database adapter. I'm developing the Rails 3 branch of Fat Free CRM. My preference is postgres, but we want the default database to be mysql2.

In this case, Gemfile.lock still needs be checked in with the default set of gems, but I need to ignore changes that I have made to it on my machine. To accomplish this, I run:

git update-index --assume-unchanged Gemfile.lock

and to reverse:

git update-index --no-assume-unchanged Gemfile.lock

It is also useful to include something like the following code in your Gemfile. This loads the appropriate database adapter gem, based on your database.yml.

# Loads the database adapter gem based on config/database.yml (Default: mysql2)
# -----------------------------------------------------------------------------
db_gems = {"mysql2"     => ["mysql2", ">= 0.2.6"],
           "postgresql" => ["pg",     ">= 0.9.0"],
           "sqlite3"    => ["sqlite3"]}
adapter = if File.exists?(db_config = File.join(File.dirname(__FILE__),"config","database.yml"))
  db = YAML.load_file(db_config)
  # Fetch the first configured adapter from config/database.yml
  (db["production"] || db["development"] || db["test"])["adapter"]
else
  "mysql2"
end
gem *db_gems[adapter]
# -----------------------------------------------------------------------------

I can't say if this is an established best practice or not, but it works well for me.

My workmates and I have different Gemfile.lock, because we use different platforms, windows and mac, and our server is linux.

We decide to remove Gemfile.lock in repo and create Gemfile.lock.server in git repo, just like database.yml. Then before deploy it on server, we copy Gemfile.lock.server to Gemfile.lock on server using cap deploy hook

Agreeing with r-dub, keep it in source control, but to me, the real benefit is this:

collaboration in identical environments (disregarding the windohs and linux/mac stuff). Before Gemfile.lock, the next dude to install the project might see all kinds of confusing errors, blaming himself, but he was just that lucky guy getting the next version of super gem, breaking existing dependencies.

Worse, this happened on the servers, getting untested version unless being disciplined and install exact version. Gemfile.lock makes this explicit, and it will explicitly tell you that your versions are different.

Note: remember to group stuff, as :development and :test

The Bundler docs address this question as well:

ORIGINAL: http://gembundler.com/v1.3/rationale.html

EDIT: http://web.archive.org/web/20160309170442/http://bundler.io/v1.3/rationale.html

See the section called "Checking Your Code into Version Control":

After developing your application for a while, check in the application together with the Gemfile and Gemfile.lock snapshot. Now, your repository has a record of the exact versions of all of the gems that you used the last time you know for sure that the application worked. Keep in mind that while your Gemfile lists only three gems (with varying degrees of version strictness), your application depends on dozens of gems, once you take into consideration all of the implicit requirements of the gems you depend on. This is important: the Gemfile.lock makes your application a single package of both your own code and the third-party code it ran the last time you know for sure that everything worked. Specifying exact versions of the third-party code you depend on in your Gemfile would not provide the same guarantee, because gems usually declare a range of versions for their dependencies. The next time you run bundle install on the same machine, bundler will see that it already has all of the dependencies you need, and skip the installation process. Do not check in the .bundle directory, or any of the files inside it. Those files are specific to each particular machine, and are used to persist installation options between runs of the bundle install command. If you have run bundle pack, the gems (although not the git gems) required by your bundle will be downloaded into vendor/cache. Bundler can run without connecting to the internet (or the RubyGems server) if all the gems you need are present in that folder and checked in to your source control. This is an optional step, and not recommended, due to the increase in size of your source control repository.

Simple answer in the year 2021: Gemfile.lock should be in the version control also for Rubygems. The accepted answer is now 11 years old.

Some reasoning here (cherry-picked from comments):

@josevalim https://github.com/heartcombo/devise/pull/3147#issuecomment-52193788

The Gemfile.lock should stay in the repository because contributors and developers should be able to fork the project and run it using versions that are guaranteed to work.

@rafaelfranca https://github.com/rails/rails/pull/18951#issuecomment-74888396

I don't think it is a good idea to ignore the lock file even for plugins. This mean that a "git clone; bundle; rake test" sequence is not guarantee to be passing because one of yours dozens of dependencies were upgraded and made your code break. Also, as @chancancode said, it make a lot harder to bisect.

Also Rails has Gemfile.lock in git:

https://github.com/rails/rails/commit/0ad6d27643057f2eccfe8351409a75a6d1bbb9d0

No Gemfile.lock means:

new contributors cannot run tests because weird things fail, so they won't contribute or get failing PRs ... bad first experience.

you cannot go back to a x year old project and fix a bug without having to update/rewrite the project if you lost your local Gemfile.lock

-> Always check in Gemfile.lock, make travis delete it if you want to be extra thorough https://grosser.it/2015/08/14/check-in-your-gemfile-lock/

A little late to the party, but answers still took me time and foreign reads to understand this problem. So I want to summarize what I have find out about the Gemfile.lock.

When you are building a Rails App, you are using certain versions of gems in your local machine. If you want to avoid errors in the production mode and other branches, you have to use that one Gemfile.lock file everywhere and tell bundler to bundle for rebuilding gems every time it changes.

If Gemfile.lock has changed on your production machine and Git doesn't let you git pull, you should write git reset --hard to avoid that file change and write git pull again.

The other answers here are correct: Yes, your Ruby app (not your Ruby gem) should include Gemfile.lock in the repo. To expand on why it should do this, read on:

I was under the mistaken notion that each env (development, test, staging, prod...) each did a bundle install to build their own Gemfile.lock. My assumption was based on the fact that Gemfile.lock does not contain any grouping data, such as :test, :prod, etc. This assumption was wrong, as I found out in a painful local problem.

Upon closer investigation, I was confused why my Jenkins build showed fetching a particular gem (ffaker, FWIW) successfully, but when the app loaded and required ffaker, it said file not found. WTF?

A little more investigation and experimenting showed what the two files do:

First it uses Gemfile.lock to go fetch all the gems, even those that won't be used in this particular env. Then it uses Gemfile to choose which of those fetched gems to actually use in this env.

So, even though it fetched the gem in the first step based on Gemfile.lock, it did NOT include in my :test environment, based on the groups in Gemfile.

The fix (in my case) was to move gem 'ffaker' from the :development group to the main group, so all env's could use it. (Or, add it only to :development, :test, as appropriate)