Heroku Buildpack for Elixir

Features

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
Pre & Post compilation hooks through pre_compile, 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)

Usage

Create a Heroku app with this buildpack

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

Set the buildpack for an existing Heroku app

heroku buildpacks:set https://github.com/HashNuke/heroku-buildpack-elixir

The above method always uses the latest version of the buildpack. To use a specific older version of the buildpack, see notes below.

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=18.2.1

# Elixir version
elixir_version=1.2.0

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

# Export heroku config vars
config_vars_to_export=(DATABASE_URL)

# A command to run right before compiling the app (after elixir, .etc)
pre_compile="pwd"

# A command to run right after compiling the app
post_compile="pwd"

# Set the path the app is run from
runtime_path="\$HOME"

# Set the subdirectory the app lives in
app_subdirectory=.

Specifying Elixir version

Use prebuilt Elixir release

elixir_version=1.2.0

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=18.2.1

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.
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
```
The buildpack will execute the commands configured in pre_compile and/or post_compile in the root directory of your application before/after it has been compiled (respectively). These scripts can be used to build or prepare things for your application, for example compiling assets.

Using older version of buildpack

Using the above methods always uses the latest version of the buildpack. We attempt to maintain the buildpack for as many old Elixir and Erlang releases as possible. But sometimes it does get hard since there's a matrix of 3 variables involved here (Erlang version, Elixir version and Heroku stack). If your application cannot be updated for some reason and requires an older version of the buildpack then use the releases page to pick a tag to use. Use the buildpack url with the tag name.

For example, if you pick the tag "v3", then the buildpack url for your app would be:

https://github.com/HashNuke/heroku-buildpack-elixir.git#v3

We only create a new tag/release when we've made breaking changes. So consider all tagged versions older than master as not recommended for use and not supported any further.

Development

Build scripts to build erlang are at https://github.com/HashNuke/heroku-buildpack-elixir-otp-builds
Sample app to test is available at https://github.com/HashNuke/heroku-buildpack-elixir-test

jwietelmann/heroku-buildpack-elixir