by hammer-corp

GitHub Readme.md

Heroku Buildpack for Elixir


  • Easy configuration with elixir_buildpack.config file
  • Use prebuilt Elixir binaries
  • DATABASE_URL can be made available at compile time adding it to config_vars_to_export in elixir_buildpack.config
  • Allows configuring Erlang
  • If your app doesn't have a Procfile, default web task mix run --no-halt will be run.
  • Consolidates protocols
  • Hex and rebar support
  • Caching of Hex packages, Mix dependencies and downloads
  • Post compilation hook through post_compile configuration

Version support

  • Erlang - Prebuilt packages (17.5, 17.4, etc)
  • Elixir - Prebuilt releases (1.0.4, 1.0.3, etc) or prebuilt branches (master, stable, etc)


Create a Heroku app with this buildpack

heroku create --buildpack "https://github.com/HashNuke/heroku-buildpack-elixir.git"

Set the buildpack of an existing Heroku app

heroku config:set BUILDPACK_URL="https://github.com/HashNuke/heroku-buildpack-elixir.git"


Create a elixir_buildpack.config file in your app's root dir. The file's syntax is bash.

If you don't specify a config option, then the default option from the buildpack's elixir_buildpack.config file will be used.

Here's a full config file with all available options:

# Erlang version

# Elixir version

# Always rebuild from scratch on every deploy?

# Export heroku config vars

# A command to run right after compiling the app

Specifying Elixir version

  • Use prebuilt Elixir release
  • Use prebuilt Elixir branch, the branch specifier ensures that it will be downloaded every time
elixir_version=(branch master)

Specifying Erlang version

  • You can specify an Erlang release version like below

Specifying config vars to export at compile time

  • To set a config var on your heroku node you can exec from the shell:
heroku config:set MY_VAR=the_value
  • Add the config vars you want to be exported in your elixir_buildpack.config file:
config_vars_to_export=(DATABASE_URL MY_VAR)

Other notes

  • Add your own Procfile to your application, else the default web task mix run --no-halt will be used.

  • If you create an application with this buildpack, then a free database addon heroku-postgresql:hobby-dev is also added. The database credentials are available from the env var DATABASE_URL.

  • Your application should build embedded and start permanent. Build embedded will consolidate protocols for a performance boost, start permanent will ensure that Heroku restarts your application if it crashes. See below for an example of how to use these features in your Mix project:

    defmodule MyApp.Mixfile do
      use Mix.Project
      def project do
        [app: :my_app,
         version: "0.0.1",
         build_embedded: Mix.env == :prod,
         start_permanent: Mix.env == :prod]
  • The buildpack will execute the command configured in post_compile in the root directory of your application after it has been compiled. This script can be used to build or prepare things for your application, for example compiling assets.


© Akash Manohar under The MIT License. Feel free to do whatever you want with it.