This is only half of the truth.
It is perfectly fine to use System.get_env in your code, whether you use distillery or mix based deployments.
You have to be careful though when you use environment variables in the config/*.exs files, they will only be evaluated at “mix-time”.
Similar caution has to be taken when reading environment variables in module attributes, but REPLACE_OS_VARS wouldn’t help there either, as distillery only hooks into the application environment at the applications boot IIRC.
