Specifying a Ruby Version
Last updated 23 October 2018
Table of Contents
Selecting a version of Ruby
You’ll need to install bundler
1.2.x or above to use the
ruby keyword and bundler
1.13.x or above to use a Ruby version specifier.
You can use the
ruby keyword in your app’s
Gemfile to specify a specific version of Ruby.
source "https://rubygems.org" ruby "2.5.1" # ...
Heroku recommends you run the latest Ruby version your app can handle. Ruby 2.5.1 might not be the latest Ruby version, and is here for demonstration purposes only. For an updated list see Supported Ruby Versions.
When you commit and push to Heroku you’ll see that Ruby
2.5.1 is detected:
-----> Heroku receiving push -----> Ruby/Rack app detected -----> Using Ruby version: 2.5.1 -----> Installing dependencies using Bundler version 1.7.11 ...
For specifying non MRI Ruby engines, you’ll need to use the
:engine_version options. You can specify JRuby by using the following line:
ruby "2.2.2", :engine => "jruby", :engine_version => "126.96.36.199"
Please see Ruby Support for a list of available versions.
Ruby Version Specifiers
As of bundler
1.12+ you can use a version specifier in your Ruby version. For example if you want to deploy using
2.3.0 but some members of your team want to use
2.3.1 you could allow this by specifying:
ruby "~> 2.3.0"
This is saying that any version of
2.3.x where x is greater than or equal to 0 are valid. For this to work on Heroku, you must specify the full version with all three digits. For example neither
~> 2.3 or
~> 2.3.x are valid version specifiers on Heroku.
Bundler locks your Ruby version you are using locally in the
Gemfile.lock. In the above scenario if someone with Ruby
2.3.1 on their system runs
bundle install then they will get this in the Gemfile.lock:
RUBY VERSION ruby 2.3.1p112
To update this version in the
Gemfile.lock, change your local Ruby version and run:
$ bundle update --ruby
The locked version of the Ruby version will always “win”. So if different members on your team are using different Ruby versions, they must be careful not to commit the wrong version to the
If you ever have doubts about the version that Heroku will use you can find out by running this command locally:
$ bundle platform --ruby
Specifying a Ruby version via the environment
Gemfile is made of up Ruby code, so you can also specify your Ruby version in the environment. For example:
ruby ENV['CUSTOM_RUBY_VERSION'] || '2.5.1'
Changing environment variables does not recompile your app. For a Ruby version change to take effect through this method, you’ll need to deploy the app again since Ruby is vendored into each slug.
This would let you specify a Ruby version in the
CUSTOM_RUBY_VERSION environment variable, or default to
2.5.1 if it’s not set. This is handy if you are running your app through a continuous integration tool and want to ensure it checks your codebase against other versions of Ruby, but restrict it to a certain version when deployed to Heroku.
We recommend limiting use of environment variables in your
Gemfile and we do not recommend using conditionals. If you need to configure things such as usernames or passwords for private repos, please see bundler configuration.
Your Ruby version is <X>, but your Gemfile specified <Y>
The most common cause of this error is the
Gemfile.lock was not updated after you modified your
Gemfile. To fix this please run
$ bundle update --ruby $ git add Gemfile.lock $ git commit -m "update ruby version"
If you are still getting an error saying that your ruby version is different than the current version specified, there are several possible causes.
First, verify that you’re using a recent version of bundler locally. We recommend running at least the same version as Heroku. You can see the version locally by running:
$ bundler -v Bundler version 1.13.6
Once you’ve verified you’re using a recent version of bundler, verify the version you’ve specified on your app by running.
$ bundle platform --ruby ruby 2.3.3p222
If this is not what you expect it to be, check inside of your
$ cat Gemfile.lock | grep -A 2 RUBY RUBY VERSION ruby 2.3.3p222
This is the version that bundler will prefer. If it is not what you want, run
bundle install locally and it will set your
Gemfile.lock ruby version to what ever you are running locally.
If when you push to Heroku, you are still getting that error make sure that you’ve committed your changes to git
$ git add Gemfile.lock $ git commit -m "Gemfile.lock ruby version"
Also verify that you’re on the
master branch of your project
$ git status -b On branch master
If you’re on a different branch than master when you run
git push heroku master this command is shortcut for
git push heroku master:master which means to send the master of your local repo to the master branch of Heroku. If you wanted to deploy a non-master branch such as
testing-feature-1 you would have to execute
git push heroku testing-feature-1:master.
A way to avoid this confusion is to set up Heroku review apps and to have a Continuous Integration (CI) server deploy to Heroku when commits are merged to master.
Applications that migrate to a non-default version of Ruby should have
bin be the first entry in their
PATH config var. The Ruby buildpack sets this value and you should not modify it. This var’s current value can be determined using
$ heroku run bash $ env | grep PATH PATH=/app/bin:/app/vendor/bundle/bin:/app/vendor/bundle/ruby/2.2.0/bin:bin:vendor/bundle/ruby/1.9.1/bin:/usr/local/bin:/usr/bin:/bin```
If absent or not the first entry you should ensure you’re using the supported version of the Ruby buildpack. If you are, please open a support ticket.
PATH is set correctly you will see the expected version using
$ heroku run "ruby -v" Running `ruby -v` attached to terminal... up, run.1 ruby 1.9.2p290 (2011-07-09 revision 32553) [x86_64-linux]
PATH is not setup correctly, you might see this error:
Your Ruby version is 1.9.2, but your Gemfile specified 1.9.3
If your PATH is setup correctly you may get this error if you have an improper hashbang (#!) line committed. For example in
bin/bundle starts with this:
#!/usr/bin/env ruby1.9.1 ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../../Gemfile', __FILE__) load Gem.bin_path('bundler', 'bundle')
It will attempt to use the wrong version of Ruby. Make sure your first line does not specify a version like this:
#!/usr/bin/env ruby ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../../Gemfile', __FILE__) load Gem.bin_path('bundler', 'bundle')
If you’re using a Bundler
1.1.4 or lower you’ll see the following error:
undefined method `ruby' for #<Bundler::Dsl:0x0000000250acb0> (NoMethodError)
You’ll need to install bundler
1.2.0 or greater to use the
$ gem install bundler