Reading Config section for 12 factor app : https://12factor.net/config it states "Another approach to config is the use of config files which are not checked into revision control" . Instead "The twelve-factor app stores config in environment variables " If not store config in source/revision control then where should config for environment variables be stored ?
For example a new developer joins a team how does that same developer access the environment variables in order to run the app ? Is it assumed an environment is provided that contains variables that allows app to run?
Where to store these is beyond the scope of 12factors, the important thing is to decouple the source repository from deployment specific data.