Managing Gems with Bundler
Last updated March 24, 2022
Table of Contents
Bundler is the default gem dependency manager for Ruby projects. Bundler is the way to manage your gems on Heroku.
Almost any gem - even those with native dependencies - can be installed using Bundler. If there’s a specific gem that won’t install on Heroku, please submit a support ticket.
To use, install bundler:
$ gem install bundler
Create a file named
Gemfile in the root of your app specifying what gems are required to run it:
source "https://rubygems.org" gem 'sinatra', '1.0'
This file should be added to the git repository since it is part of the app. You should also add the
.bundle directory to your
.gitignore file. Once you have added the
Gemfile, it makes it easy for other developers to get their environment ready to run the app:
$ bundle install -j4
This ensures that all gems specified in
Gemfile, together with their dependencies, are available for your application. Running
bundle install also generates a
Gemfile.lock file, which should be added to your git repository.
Gemfile.lock ensures that your deployed versions of gems on Heroku match the version installed locally on your development machine. The flag
-j4 will use 4 parallel jobs to install all of your dependencies. This feature was introduced in bundler 1.5.0
platforms section of your
Gemfile contains Windows entries, such as
mingw, then the
Gemfile.lock file will be ignored.
Heroku also uses that file to resolve and install your application dependencies automatically. All you need to do is to push it:
-----> Heroku receiving push -----> Sinatra app detected -----> Gemfile detected, running Bundler version 1.5.2 Unresolved dependencies detected; Installing... Using rack (1.2.1) Using sinatra (1.0) Using bundler (1.0.0) Your bundle is complete! Use `bundle show [gemname]` to see where a bundled gem is installed. Your bundle was installed to `.bundle/gems` Compiled slug size is 10.7MB -----> Launching.... done
Specifying gems and groups
The recommended use of gem bundler is to bundle absolutely every gem your app depends upon. This includes your framework (Rails, Sinatra, etc) and your database connectors.
Bundling Rails and other dependencies does increase your slug size by a few megabytes. Increased slug size is a worthwhile tradeoff for vastly simplified dependency management, as well as the flexibility of being able to use any version of Rails you wish.
To specify groups of gems to not to be installed, you can use the
BUNDLE_WITHOUT config var.
$ heroku config:set BUNDLE_WITHOUT="development:test"
Using Bundler with Rails 3
Rails 3 is built on top of Bundler. That means there is no setup needed, all gems specified on the
Gemfile are ready for use on your app.
Using Bundler with Rails 2.3.X
Follow the instructions here. Remember to remove all your
config.gem lines from your environment configuration file! Also remember to specify the appropriate database gem for your app.
gem "pg", :group => :production gem "sqlite3-ruby", :group => :development
After you have added the code to your application, run
$ bundle install
And your app is running with Bundler.
Using Bundler from Sinatra (or Other Rack Apps)
Gembundler has a great set of documentation on how to use Bundler with Sinatra and other frameworks as well.
Versions of Bundler
See Bundler Version about using different versions of Bundler.