Deploy a Phoenix App with Distillery

This is a guide to deploying Phoenix projects on Render using Distillery.

We’ll start off with a bare Phoenix project with Ecto, modify it to use Distillery, and deploy it on Render. The full source code for this tutorial is available at https://github.com/render-examples/phoenix-distillery.

Create a Phoenix App with Distillery

1. Create a new Phoenix app in the terminal.

   mix phx.new phoenix_distillery # also fetch and install dependencies
   cd phoenix_distillery

2. Update mix.exs to add Distillery to deps.

   defp deps do
      [ ...,
        {:distillery, "~> 2.0"}
      ]

   Then run mix deps.get in your terminal to update dependencies.

Configure Distillery

1. Let’s configure Distillery for production. Update the Endpoint config in config/prod.exs so it looks like this:

   config :phoenix_distillery, PhoenixDistilleryWeb.Endpoint,
     cache_static_manifest: "priv/static/cache_manifest.json",
     server: true, # critical for Phoenix to run
     root: ".",
     version: Application.spec(:phoenix_distillery, :vsn)

   Read more about Distillery configuration.

   We’re not going to check secrets into source control. Instead, we’re going to manage them in production with Render environment variables. So let’s delete the line at the end referring to prod.secret.exs.

   import_config "prod.secret.exs" # delete me

   And delete the file config/prod.secret.exs.

2. You’re now ready to initialize your Distillery release.

   mix distillery.init

   This will create rel/config.exs, rel/vm.args, and the empty directory rel/plugins.

   rel/vm.args is used for runtime configuration by default, but we’re going to use the Mix Config Provider instead so you can delete this file.

Creating a Mix Config Provider

1. Create a Mix configuration file at rel/config/config.exs:

   mkdir -p rel/config

   Contents of rel/config/config.exs :

   use Mix.Config
   
   port = String.to_integer(System.get_env("PORT") || "4000")
   default_secret_key_base = :crypto.strong_rand_bytes(43) |> Base.encode64
   
   config :phoenix_distillery, PhoenixDistilleryWeb.Endpoint,
     http: [port: port],
     url: [host: "localhost", port: port],
     secret_key_base: System.get_env("SECRET_KEY_BASE") || default_secret_key_base

   This sets up the Mix configuration provider to get values from runtime environment variables.

2. Update rel/config.exs to use your new provider. Change the environment :prod section in the file to this:

   environment :prod do
     set include_erts: true
     set include_src: false
     set cookie: :"GZUAPxTBG1]F%gaBG6.|Fxqpi^]dVX>:AFn^YxR/RY%KE1ys/l6$cd3}8r4h$B4E"
     set config_providers: [    {Distillery.Releases.Config.Providers.Elixir, ["${RELEASE_ROOT_DIR}/etc/config.exs"]}  ]  set overlays: [    {:copy, "rel/config/config.exs", "etc/config.exs"}  ]end

Configuring Ecto

Let’s configure Ecto to get the DATABASE_URL from the environment. Change lib/phoenix_distillery/repo.ex so it looks like this:

defmodule PhoenixDistillery.Repo do
  use Ecto.Repo,
    otp_app: :phoenix_distillery,
    adapter: Ecto.Adapters.Postgres,    pool_size: 10  def init(_type, config) do    {:ok, Keyword.put(config, :url, System.get_env("DATABASE_URL"))}  endend

This way Ecto gets database connection information from runtime environment variables.

Build a Release with Distillery

You’re now ready to build and run your first release!

npm run deploy --prefix assets && MIX_ENV=prod mix do phx.digest, distillery.release --env=prod

The output should look like this:

==> Assembling release..
==> Building release phoenix_distillery:0.1.0 using environment prod
==> Including ERTS 10.4.4 from /usr/local/Cellar/erlang/22.0.7/lib/erlang/erts-10.4.4
==> Packaging release..
Release successfully built!
To start the release you have built, you can use one of the following tasks:

 # start a shell, like 'iex -S mix'
 > _build/prod/rel/phoenix_distillery/bin/phoenix_distillery console

 # start in the foreground, like 'mix run --no-halt'
 > _build/prod/rel/phoenix_distillery/bin/phoenix_distillery foreground

 # start in the background, must be stopped with the 'stop' command
 > _build/prod/rel/phoenix_distillery/bin/phoenix_distillery start

 If you started a release elsewhere, and wish to connect to it:

 # connects a local shell to the running node
 > _build/prod/rel/phoenix_distillery/bin/phoenix_distillery remote_console

 # connects directly to the running node's console
 > _build/prod/rel/phoenix_distillery/bin/phoenix_distillery attach

For a complete listing of commands and their use:

 > _build/prod/rel/phoenix_distillery/bin/phoenix_distillery help

You can now test your release (assuming PostgreSQL is up on your local machine):

export DATABASE_URL=postgres://username:password@127.0.0.1:5432/phoenix_distillery
_build/prod/rel/phoenix_distillery/bin/phoenix_distillery foreground

12:00:00.123 [info] Running PhoenixDistilleryWeb.Endpoint with cowboy 2.6.1 at http://localhost:4000

You can now deploy your app in production! 🎉

Deploying to Render

1. Create a build script called build.sh at the root of your repo:

   #!/usr/bin/env bash
   # exit on error
   set -o errexit
   
   export MIX_ENV=prod
   
   # get app name and version from mix.exs
   export APP_NAME="$(grep 'app:' mix.exs | sed -e 's/\[//g' -e 's/ //g' -e 's/app://' -e 's/[:,]//g')"
   export APP_VSN="$(grep 'version:' mix.exs | cut -d '"' -f2)"
   
   # remove existing builds
   rm -rf "_build"
   
   # Compile app and assets
   mix deps.get --only prod
   mix compile
   cd assets && npm install && npm run deploy && cd ..
   
   # create release
   # we don't need to create a tarball because the app will be
   # served directly from the build directory
   mix do phx.digest, distillery.release --env=prod --no-tar
   
   echo "Linking release $APP_NAME:$APP_VSN to _render/"
   
   ln -sf "_build/$MIX_ENV/rel/$APP_NAME" _render

   Make the script executable before checking it into Git:

   chmod a+x build.sh

2. Create a new PostgreSQL database on Render.

3. Create a new Web Service on Render, and give Render permission to access your new repo.

4. Use the following values during creation:

   Runtime	Elixir
   Build Command	./build.sh
   Start Command	./_render/bin/phoenix_distillery foreground

   Under the Advanced section, add two new environment variables:

   Key	Value
   SECRET_KEY_BASE	A sufficiently strong secret. You can generate a secret locally by running mix phx.gen.secret
   DATABASE_URL	The internal database URL of the database you created above.

That’s it! Your web service will be live on your Render URL as soon as the build finishes.

Going forward, every push to your repo will automatically build your app and deploy it in production. If the build fails, Render will automatically stop the deploy process and the existing version of your app will keep running until the next successful deploy.

Read about customizing Elixir and Erlang versions for your app.