Heroku Buildpack for Elixir

Features

Easy configuration with elixir_buildpack.config file
Use prebuilt Elixir binaries
Adds the free Heroku Postgres database upon app creation
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 server -p $PORT will be run.
Consolidates protocols
Hex and rebar support
Caching of Hex packages, Mix dependencies and downloads

Version support info

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

Usage

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"

Configuration

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
erlang_version=17.5

# Elixir version
elixir_version=1.0.4

# Always rebuild from scratch on every deploy?
always_rebuild=false

# Export heroku config vars
config_vars_to_export=(DATABASE_URL)

Specifying Elixir version

Use prebuilt Elixir release

elixir_version=1.0.4

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

erlang_version=17.5

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]
  end
end

andreasknoepfle / heroku-buildpack-elixir