The releases.exs file was released in elixir 1.9, this was the first attempt at runtime config but it only applied to releases and not in dev. Elixir 1.11 introduced runtime.exs which runs in both dev and release mode.

To clarify this further. In elixir any code, which is not within a function definition (or moved to such via a macro) will be executed at compile time.

The issue is here. These lines that are at the bottom of the file will be executed at compile time. Thus runtime.exs will not be evaluated yet. Any values set in runtime.exs are only available at runtime.

I wrote this blog post that attempts to clarify the differences between the configurations (in the article I call “compile time” “build time” but it means the same thing): Elixir: Time for Some Configuration – Random Notes

To simplify, if you want to see your values from runtime.exs, you need to grab them at runtime, i.e. inside a function that is called at runtime.

I think the easiest way that you can check your config here, would be to start the app like iex -S mix and call Application.fetch_env(:myapp, :jon) inside iex

So basically try this:

defmodule MyApp.Application do
  use Application

  def start(_type, _args) do
    IO.inspect(Application.get_all_env(:myapp))
    # ...
  end
end