Indeed, the whole point of the 12 factor design is to decouple the app from a single config file. Instead you use whatever method you like to define environment

Indeed, the whole point of the 12 factor design is to decouple the app from a single config file. Instead you use whatever method you like to define environment variables and the app should just work. Also helps avoid committing secrets to your git repo. I use SystemD extensively and it's pretty neat, you just: - Define default Environment variables in your unit file - Customize a service by adding an overrides.conf file in foo.service.d/ folder This makes it easy to define exactly the environment for a service. .env files are helpful in dev mode to customise machines where I don't want to pollute the system env, but they aren't the 'config format' and it makes sense that they are specific to the OS/shell they need to run in.