Configuration and Secrets

Gigalixir auto-detects that you want to use Elixir Releases if you have a config/releases.exs file, so let’s create one.

Elixir 1.11 adds config/runtime.exs. If you use that instead, then you’ll want to specify buildpacks since we can no longer detect if you want releases or mix mode. See buildpacks-releases.

echo "import Config" > config/releases.exs

The only configuration change we really need to do now is make sure the web server is started. Therefore, add the following to your releases.exs.

config :gigalixir_getting_started, GigalixirGettingStartedWeb.Endpoint,
  server: true,
  http: [port: {:system, "PORT"}], # Needed for Phoenix 1.2 and 1.4. Doesn't hurt for 1.3.
  url: [host: System.get_env("APP_NAME") <> "", port: 443]
  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.

If you’re using a free tier database, be sure to also set your pool size to 2 in prod.exs.

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


Let’s make sure everything works.

First, try building static assets:

mix deps.get
cd assets
npm install
npm run deploy
cd ..
mix phx.digest

and building a release locally:

export SECRET_KEY_BASE="$(mix phx.gen.secret)"
export DATABASE_URL="postgresql://user:pass@localhost:5432/foo"
MIX_ENV=prod mix release

and running it locally:

MIX_ENV=prod APP_NAME=gigalixir_getting_started PORT=4000 _build/prod/rel/gigalixir_getting_started/bin/gigalixir_getting_started start

Don’t forget to replace gigalixir_getting_started with your own app name. Also, change/add the environment variables as needed.

Check it out to see if it’s successfull:

curl localhost:4000

If that didn’t work, the first place to check is prod.exs. Make sure you have server: true somewhere and there are no typos.

Also check out troubleshooting.

If it still doesn’t work, don’t hesitate to contact our Support.

If everything works, commit the changes:

git add config/prod.exs assets/package-lock.json config/releases.exs
git commit -m 'releases configuration'

Then continue on 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,


It’s important that you do not include release=true in your elixir_buildpack.config. The causes the elixir buildpack to generate a release which conflicts with the release generated by gigalixir-buildpack-releases.


If you need to configure your release in mix.exs make sure the release name matches your app name (also defined in mix.exs, not your Gigalixir app name).

gigalixir-buildpack-phoenix-static is optional if you do not have Phoenix static assets.

For more information about buildpacks, see the 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-releases, then the command run will be /app/bin/foo start.
  • If the last buildpack is gigalixir-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.