Switch to a config file per app instead of a config file per environment

Hi,

There are a few writeups describing alternative config arrangements by a topic (or an OTP app):

• Configuring Phoenix apps: Two small adjustments with big effects | bitcrowd blog
• Tips for improving your Elixir configuration

I tried it out on a hobby project and found it more convenient than a configuration per environment, and therefore, I’d like to propose changing the default.

In my case, the whole of config.exs was just five lines long

import Config

for config_file <- Path.wildcard(Path.join([File.cwd!(), "config", "compile_time", "*.exs"])) do
  import_config(config_file)
end

The longest file in the compile_time dir, the endpoint configuration was

import Config

config :my_app, MyAppWeb.Endpoint,
  url: [host: "localhost"],
  render_errors: [
    formats: [html: MyAppWeb.ErrorHTML, json: MyAppWeb.ErrorJSON],
    layout: false
  ],
  pubsub_server: MyApp.PubSub,
  live_view: [signing_salt: "tU71HhHQ"]

case config_env() do
  :dev ->
    config :my_app, MyAppWeb.Endpoint,
      http: [ip: {127, 0, 0, 1}, port: 4001],
      check_origin: false,
      code_reloader: true,
      debug_errors: true,
      secret_key_base: "ztwTR1eV8qJmsKqFsAHcSu49my17XV5KULr6okIBXz9aRJEc4t8L2q3okO1L+ujE",
      watchers: [
        esbuild: {Esbuild, :install_and_run, [:default, ~w(--sourcemap=inline --watch)]},
        tailwind: {Tailwind, :install_and_run, [:default, ~w(--watch)]}
      ]

    config :my_app, MyAppWeb.Endpoint,
      live_reload: [
        patterns: [
          ~r"priv/static/.*(js|css|png|jpeg|jpg|gif|svg)$",
          ~r"priv/gettext/.*(po)$",
          ~r"lib/my_app_web/(controllers|live|components)/.*(ex|heex)$"
        ]
      ]

  :test ->
    config :my_app, MyAppWeb.Endpoint,
      http: [ip: {127, 0, 0, 1}, port: 4002],
      secret_key_base: "oKSvXrmhGIz0TZUqB5PzlzJREnh7I1+TMCyWlvEhCR/AgN3jec4kl2s+qTkZsqTP",
      server: false

  _ ->
    :ok
end

I also split runtime.exs under config/runtime, which required a bit more ceremony:

• figure out where from configs should be read (source vs release
• copying runtime configs during release assembly.

# config/runtime.exs
import Config

topic_configs_path =
  if config_env() == :prod do
    root_dir = :code.priv_dir(:my_app)
    release_version = Application.spec(:my_app, :vsn) |> to_string()

    runtime_path =
      [root_dir, "..", "..", "..", "releases", release_version, "runtime"]
      |> Path.join()
      |> Path.expand()

    Path.join([runtime_path, "*.exs"])
  else
    Path.join([File.cwd!(), "config", "runtime", "*.exs"])
  end

for config_file <- Path.wildcard(topic_configs_path) do
  Code.require_file(config_file)
end

defmodule MyApp.MixProject do
  def project do
    [
      releases: [
        sesame: [
          steps: [:assemble, &copy_prod_runtime_configs/1],
        ]
      ]
    ]
  end
 defp copy_prod_runtime_configs(%Mix.Release{version_path: path} = release) do
    release_config_dir = "runtime"
    File.mkdir!(Path.join([path, release_config_dir]))

    all_configs =
      [File.cwd!(), "config", "runtime", "*.exs"]
      |> Path.join()
      |> Path.wildcard()

    for config_file <- all_configs do
      dst_path = Path.join([path, release_config_dir, Path.basename(config_file)])
      Logger.info("COPYING #{config_file} as #{dst_path} ")

      File.cp!(
        config_file,
        dst_path
      )
    end

    release
  end

Btw, if anyone have suggestions on better ways to get a releases directory than

root_dir = :code.priv_dir(:my_app)
release_version = Application.spec(:my_app, :vsn) |> to_string()

runtime_path =
      [root_dir, "..", "..", "..", "releases", release_version, "runtime"]
      |> Path.join()
      |> Path.expand()

that would be a very welcomed change