Using Mix

For an example app that uses mix and works on gigalixir, see

Configuration and Secrets

Then append something like the following in prod.exs. Don’t replace what you already have, just add this to the bottom.

config :gigalixir_getting_started, GigalixirGettingStartedWeb.Endpoint,
  http: [port: {:system, "PORT"}], # Possibly not needed, but doesn't hurt
  url: [nil, port: 80],
  secret_key_base: Map.fetch!(System.get_env(), "SECRET_KEY_BASE"),
  server: true

config :gigalixir_getting_started, GigalixirGettingStarted.Repo,
  adapter: Ecto.Adapters.Postgres,
  url: System.get_env("DATABASE_URL"),
  ssl: true,
  pool_size: 2 # Free tier db only allows 4 connections. Rolling deploys need pool_size*(n+1) connections where n is the number of app replicas.
  1. Replace :gigalixir_getting_started with your app name e.g. :my_app

  2. Replace GigalixirGettingStartedWeb.Endpoint with your endpoint module name. You can find your endpoint module name by running something like

    grep -R "defmodule.*Endpoint" lib/

    Phoenix 1.2, 1.3, and 1.4 give different names so this is a common source of errors.

  3. Replace GigalixirGettingStarted.Repo with your repo module name e.g. MyApp.Repo

You don’t have to worry about setting your SECRET_KEY_BASE config because we generate one and set it for you.

Don’t forget to commit your changes

git add config/prod.exs
git commit -m "setup production deploys"


Let’s make sure everything works.

APP_NAME=foo SECRET_KEY_BASE="$(mix phx.gen.secret)" MIX_ENV=prod DATABASE_URL="postgresql://user:pass@localhost:5432/foo" PORT=4000 mix phx.server

Check it out.

curl localhost:4000

If everything works, continue to Set Up App for Deploys.

Specify Buildpacks (optional)

We rely on buildpacks to compile and build your release. We auto-detect a variety of buildpacks so you probably don’t need this, but if you want to specify your own buildpacks create a .buildpacks file with the buildpacks you want. For example,

heroku-buildpack-phoenix-static is optional if you do not have Phoenix static assets. For more information about buildpacks, see Life of a Deploy.

Note, that the command that gets run in production depends on what your last buildpack is.

  • If the last buildpack is gigalixir-buildpack-mix, then the command run will be something like elixir --name $MY_NODE_NAME --cookie $MY_COOKIE -S mix phx.server.
  • If the last buildpack is heroku-buildpack-phoenix-static, then the command run will be mix phx.server.
  • If the last buildpack is heroku-buildpack-elixir, then the command run will be mix run --no-halt.

If your command is mix run --no-halt, but you are running Phoenix (just not the assets pipeline), make sure you set server: true in prod.exs.

We highly recommend keeping gigalixir-buildpack-mix last so that your node name and cookie are set properly. Without those, remote_console, ps:migrate, observer, etc won’t work.