Deploying Elixir/Phoenix

18 July 2016

This page is something of a living blog post, and it does get updated from time to time. I suggest you look at the file’s history if you need to know how fresh/stale this guide is.

Well 314, it has been a while, has it not? I have recently completed a bit of an adventure (or completed the adventure nearly enough to share, at any rate). I’ve gone and fallen in love with the Elixir programming language, and the star of the Elixir world right now is Phoenix, a web framework. Now, cutting websites it’s nearly as sexy as it was in the late nineties, but this nearly makes up for it.

Phoenix’s one-two punch of a Rails-ish paradigm and a nice database layer in Ecto makes it a true joy to work with. Where Phoenix gains on Rails, however, is in Elixir, a language which keeps much of the happiness of Ruby while handing you the speed of Erlang. Even on database-backed pages Phoenix returns pages in tens of milliseconds.

So it’s some hot stuff, and it makes me happy. But with all web apps, there comes a time when running it on my laptop is not enough. So I embarked upon a journey to learn to deploy Elixir/Phoenix apps to a server using edeliver and exrm.

The overall model of deployment is to commit and push code to your source repository. edeliver will then pull that to a build server (a server that resembles your production server - in OS and architecture, so you can build a compatible package). On this build server it uses exrm to compile a release (or upgrade, which can patch your running code - pretty dope), and downloads that to your computer. You then upload this package to your production server(s).

These exrm releases themselves are pretty cool. They are self-contained releases, they include an Erlang VM, all the package and dependencies to make your app run. Gone are the days of hammering from three dozen machines every deploy!

For my build server, I simply set up a new user account on my Digital Ocean droplet, running Ubuntu Linux, which runs this site and my IRC bouncer. My production server was similarly yet another account on this server. edeliver, however, supports a plurality of production servers. Cleverly, it uses SSH, so you can use keys to make things happen without a single password getting in the way.

Setting up a Build Server

SSH to the server as root or any sudo-capable user.

We’ll be using asdf to manage our development dependencies (erlang, elixir, and nodejs). This allows us to install a plurality of versions in case you have to build different projects requiring different versions from the same build user.

First we’ll install some prerequisites via apt.

sudo apt-get install -y git vim unzip \
    build-essential autoconf m4 libncurses5-dev \
    libwxgtk3.0-dev libgl1-mesa-dev libglu1-mesa-dev \
    libpng3 libssh-dev unixodbc-dev
sudo update-alternatives --set editor /usr/bin/vim.basic

Now create a build user.

sudo useradd --shell=/bin/bash build

You should install any applicable SSH key for the build user into ~build/.ssh/authorized_keys now.

Login as the build user now and install asdf and its plugins.

git clone ~/.asdf
echo '. $HOME/.asdf/' >> ~/.profile
echo '. $HOME/.asdf/completions/asdf.bash' >> ~/.profile
source ~/.profile
asdf plugin-add erlang
asdf plugin-add elixir
asdf plugin-add nodejs

This next step will install the actual tools. This can take a while, so I suggest separating each command by a comma, then running off to get something to eat. It can take a moment.

asdf install erlang 19.0
asdf global  erlang 19.0
asdf install elixir 1.3.1
asdf global  elixir 1.3.1
asdf install nodejs 6.3.1
addf global  nodejs 6.3.1

Note: Erlang requires somewhere slightly north of 1GB of RAM to build successfully, or it dies somewhere in a WxWidgets library compile. I suggest that you enable a swapfile during the build if you have less than 2GB of free RAM before starting the build. As this will degrade the SSD hardware you’re probably running on, I suggest you remove the swapfile after the build is completed.

If this worked, then installing Hex and Rebar will work.

mix local.hex
mix local.rebar

Your build server is almost ready to get to work! Create the my-app_prod.secret.exs file, which should follow the following template.

vim my-app_prod.secret.exs
  use Mix.Config

  config :my_app, MyApp.Repo,
    adapter: Ecto.Adapters.Postgres,
    username: "u",
    password: "p",
    database: "d",
    hostname: "localhost",
    template: "template0",
    pool_size: 10

I’ll leave the configuration of your PostgreSQL server to you - there are plenty of tutorials and how-to’s for it. Suffice it to say, you should substitute real values where I have left placeholders.

Setting up a Production Server

Some of these steps will be identical to the steps performed on the build server. If these servers are the same, you can safely skip the redundant steps.

First, SSH to the new production server as root or a sudo-capable user. First we’ll install Elixir and some Erlang dependencies, as well as PostgreSQL. Again, if this isn’t your database host, then you might try omitting some. Also, I’m not too sure if the Erlang dependencies are even necessary. If someone does know, please drop me a message.

sudo useradd -s /bin/bash my-app
sudo mkdir -p ~my-app/.ssh
# add relevant keys to ~my-app/.ssh/authorized_keys
sudo chown -R my-app:users ~my-app

On deploy and start the application will be running on port 4001 or whatever port you configure in your prod.exs file, so firewall that sucker up.

sudo ufw deny 4001

Next configure Nginx to reverse proxy to port 4001. Be sure to replace the IP address with the public IP address of your production server.

sudo vim /etc/nginx/sites-available/
  map $http_upgrade $connection_upgrade {
    default upgrade;
    '' close;

  server {
    listen 80;

    access_log off;

    location /.well-known {
      root /var/www/letsencrypt;
      try_files $uri /dev/null =404;

    location / {
      return 301 https://$host$request_uri;

  server {
    listen 443 ssl http2;
    access_log off;

    ssl_certificate /etc/letsencrypt/live/;
    ssl_certificate_key /etc/letsencrypt/live/;

    location / {

      include proxy_params;

      proxy_set_header Upgrade $http_upgrade;
      proxy_set_header Connection $connection_upgrade;
sudo ln -s /etc/nginx/sites-{available,enabled}/
sudo service nginx reload

Finally, set the app to autostart on machine boot. So that random things like rebooting for a kernel update doesn’t leave the app high and dry until someone pokes you on Slack.

sudo vim /etc/init.d/my-app-prod.conf
  description "my-app-prod"

  ## Uncomment the following two lines to run the
  ## application as www-data:www-data
  setuid my-app
  setgid my-app

  start on runlevel [2345]
  stop on runlevel [016]

  expect stop

  env MIX_ENV=prod
  export MIX_ENV

  ## Uncomment the following two lines if we configured
  ## our port with an environment variable.
  # env PORT=4001
  # export PORT

  env HOME=/home/my-app/my_app
  export HOME

  pre-start exec /bin/sh /home/my-app/my_app/bin/my_app start

  post-stop exec /bin/sh /home/my-app/my_app/bin/my_app stop

Configuring your Phoenix Project

There isn’t a whole lot to do here, but some of these steps are important and missing one can lead to about a day of very confused debugging.

vim config/prod.exs
  use Mix.Config

  config :my_app, MyApp.Endpoint,
    http: [port: 4001], # configure the port to rproxy to here!
    url: [host: "", port: 80],
    cache_static_manifest: "priv/static/manifest.json",
    server: true # DON'T FORGET THIS LINE

  config :logger, level: :info

  import_config "prod.secret.exs"

There will be a mess of comments in there, I haven’t explored what they all do yet.

The next file to change is mix.exs, which you need to add edeliver to as a dependency.

vim mix.exs
  # ...

  def application do
    [mod: {MyApp, []},
     applications: [:phoenix, :phoenix_pubsub, :phoenix_html, :cowboy,
                    :logger, :gettext, :phoenix_ecto, :postgrex, :edeliver]]

  # ...

  defp deps do
    [{:phoenix, "~> 1.2.0"},
     {:postgrex, ">= 0.11.2"},
     {:phoenix_ecto, "~> 3.0"},
     {:phoenix_html, "~> 2.6.1"},
     {:phoenix_live_reload, "~> 1.0.5", only: :dev},
     {:gettext, "~> 0.11"},
     {:cowboy, "~> 1.0.4"},
     {:edeliver, "~> 1.2.10"}]

You’ll notice that we’ve added edeliver to both applications and deps. Note that there is a release version in this file. You can and should increment that from time to time. It’ll show up in your builds - speaking of which, we need to configure edeliver to know about all the work we’ve just done! Do this by creating an edeliver configuration file, that should look something like this:

mkdir -p .deliver
vim .deliver/config
  #!/usr/bin/env bash

  APP="my_app" # name of your release

  # You can experiment around with this to see what you like best.
  # I'm a retard, so I build a lot without incrementing the version
  # number, so I like having the extra info. More disciplined developers
  # can probably forgo that, however.

  BUILD_HOST="" # host where to build the release
  BUILD_USER="build" # local user at build host
  BUILD_AT="/home/build/builds/my_app" # build directory on build host

  # I don't use any staging servers, so these are really kind of
  # moot point for me. #YOLO


  # runs the phoenix.digest mix command, which gets rid of a missing
  # manifest file error
  pre_erlang_clean_compile() {
    status "Installing NodeJS dependencies"
    __sync_remote "
      [ -f ~/.profile ] && source ~/.profile # load profile (optional)
      set -e # fail if any command fails (recommended)
      cd '$BUILD_AT' # enter the build directory on the build host (required)
      # prepare something
      mkdir -p priv/static # required by the phoenix.digest task
      # run your custom task
      APP='$APP' MIX_ENV='$TARGET_MIX_ENV' npm install
    status "Building frontend items"
    __sync_remote "
      [ -f ~/.profile ] && source ~/.profile # load profile (optional)
      set -e # fail if any command fails (recommended)
      cd '$BUILD_AT' # enter the build directory on the build host (required)
      # prepare something
      mkdir -p priv/static # required by the phoenix.digest task
      # run your custom task
      APP='$APP' MIX_ENV='$TARGET_MIX_ENV' npm run deploy
    status "Running phoenix.digest" # log output prepended with "----->"
    __sync_remote " # runs the commands on the build host
      [ -f ~/.profile ] && source ~/.profile # load profile (optional)
      set -e # fail if any command fails (recommended)
      cd '$BUILD_AT' # enter the build directory on the build host (required)
      # prepare something
      mkdir -p priv/static # required by the phoenix.digest task
      # run your custom task
      APP='$APP' MIX_ENV='$TARGET_MIX_ENV' $MIX_CMD phoenix.digest $SILENCE

  # copies the prod.secret.exs file you keep sequestered on your build
  # machine into the build directory.
  pre_erlang_get_and_update_deps() {
    # copy it on the build host to the build directory when building
    local _secret_config_file_on_build_host="/home/build/my-app_prod.secret.exs"
    if [ "$TARGET_MIX_ENV" = "prod" ]; then
      status "Linking '$_secret_config_file_on_build_host' to build config dir"
      __sync_remote "
        ln -sfn '$_secret_config_file_on_build_host' '$BUILD_AT/config/prod.secret.exs'

Building and Deploying a Release

All this work, and it boils down to some very simple commands!

mix edeliver build release

Copy the release tag from the output, and deploy that sucker.

mix edeliver deploy release to production --version=<<that release tag>>
mix edeliver start production
mix edeliver migrate production # runs your database migrations!

All that work, but look at what was gained! A very slick deployment process that encourages sustainable versioning. These have been my notes from the adventure, which I hope you benefit from in some way. If you find any error, I encourage you to let me know, preferably by making a pull request on this file with the fix.

Happy coding, and more importantly, happy deploying, 314!