Getting rid of Mix related code in Elixir Releases - deployment

Question

I am developing an elixir application and deploying that application via Elixir Releases and Docker. All of that is going fine and I can use environment variables for runtime configuration.
For local development I wanted to use dotenv and the way I'd like to set up my project is that I want to read configuration from my config/*.exs files.
Now I found out that Mix is not available in Elixir releases so the proposed solution of dotenv for configuring .exs files via environment variables will fail on production start.
defmodule App.Application do
use Application
def start(_type, _args) do
unless Mix.env == :prod do
Dotenv.load
Mix.Task.run("loadconfig")
end
# ... the rest of your application startup
end
end
Result
(UndefinedFunctionError) function Mix.env/0 is undefined (module Mix is not available)
I was wondering if I can just on compile time determine whether I'm in production mode and just leave out the dotenv load section:
I came up with this:
defmodule Roundhay.Application do
def start(_type, _args) do
quote do
unquote(unless Mix.env() == :prod, do: load_env())
end
# load rest of application
end
defp load_env do
Dotenv.load()
Mix.Task.run("loadconfig")
end
end
But that just yields the same problem.
Is there any way I can just omit the whole block existing when compiling in production mode?

Answer 1

Did you read the top section of the docs you linked to?
WARNING: Not compatible with Elixir releases
It seems like what you're trying to do is not supported by that library, because it fundamentally relies on Mix being available at runtime.
There is also a comment on a closed issue recommending against trying to use macros, as you are doing:
It is entirely possible that you could inject your secrets into the
compiled result through macro use. It would totally possible without
realizing you had done it.
Additionally, many apps do not build in the same environment they
deploy, and this has caused issues repeatedly for users of this
library, who inadvertently inject values into the compiled result that
are blank because a macro inserted them at compile time but they are
only available at run time in the production environment
Another way you could do it is to follow standard Elixir patterns for config, and use a tool like tool like direnv to set your environment for running the release locally.