Distillery config provider

environment_config_provider.ex

defmodule EnvironmentConfigProvider do
  use Mix.Releases.Config.Provider

  @impl Provider
  def init(%{env_var_name: var_name, persist: [app, config_variable]}) do
    value = System.get_env(var_name) || raise "No value provided for ENV variable #{var_name}"
    Application.put_env(app, config_variable, value, persistent: true)
  end
end