Using docker environment variables instead of .env files

I want to deploy Shopware to Dokku which all goes pretty well. Except when it comes to reading the environment variables.

With Dokku (open source heroku) you can set the env variables which are injected into the docker container. I can see all the set variables when entering the container. However, every deploy I do removes the .env.local which was created during install and the install starts over.

So how can I make sure it does not look for the `.env’ files and instead uses the already available ones?

Not terribly unimportant, which are the most important variables to set?

According to the Symfony documentation, environment variables do override the .env.locale, thus you can ignore the .env.local