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Elixir buildpack for Heroku.
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Heroku buildpack: Elixir

This is a Heroku buildpack for Elixir apps. It uses Mix.

Configure your Heroku App

$ heroku config:add BUILDPACK_URL="" -a YOUR_APP


$ heroku create --buildpack ""

Select an Erlang version

The Erlang/OTP release version that will be used to build and run your application is now sourced from a dotfile called .preferred_otp_version. It needs to be the branch or tag name from the repository, and further, needs to be one of the versions that precompiled binaries are available for.

Currently supported OTP versions:

  • master (R17A)
  • OTP_R16B02
  • OTP_R16B01
  • OTP_R16B
  • OTP_R15B03
  • OTP_R15B02
  • OTP_R15B01

To select the version for your app:

$ echo OTP_R16B02 > .preferred_otp_version
$ git commit -m "Select R16B02 as preferred OTP version" .preferred_otp_version

If no version is explicitly specified, master will be used.

Select an Elixir version

The application will be compiled and run using Elixir master and Mix.

You can specify custom branch or tag name from the repository in the .preferred_elixir_version dotfile.

Setup a Procfile

Heroku needs a Procfile in order to run your application. Create a Procfile with a web process defined:


$ echo 'web: mix server -p $PORT' > Procfile

The buildpack sets MIX_ENV=prod so you don't have to.

Important Note: Single quotes are important here. $PORT is an environment variable supplied by Heroku. If you use double quotes in the above echo call, your local shell will try to interpolate the contents, and you'll end up with -p and not -p $PORT.


$ echo 'web: mix run --no-halt' > Procfile

You should bind to port specified in PORT environment variable:

{ :ok, _ } = :cowboy.start_http(
  :http, 100,
  [port: port(System.get_env("PORT"))],
  [env: [dispatch: dispatch]]
def port(nil), do: 8080
def port(value) do

Important Note: If you bind to any other port than the assigned one, your process will be killed with an R11 error code.


heroku-elixir-buildpack supports only applications which use Mix to manage dependencies.

Build your Heroku App

$ git push heroku master

You may need to write a new commit and push if your code was already up to date.

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