4 is possible. You run the app locally using foreman, store your local variables in a .env file, and add that to your gitignore. For your heroku running app,

4 is possible. You run the app locally using foreman, store your local variables in a .env file, and add that to your gitignore. For your heroku running app, you use the toolbelt to add env variables. https://devcenter.heroku.com/articles/config-vars#local-setup https://devcenter.heroku.com/articles/config-vars#local-setu... https://devcenter.heroku.com/articles/config-vars#setting-up-config-vars-for-a-deployed-application https://devcenter.heroku.com/articles/config-vars#setting-up...