It's not 'someone else'. It's whatever environment the application ends up running in. The idea of 12 factor is to define a reasonable interface for your appli

It's not 'someone else'. It's whatever environment the application ends up running in. The idea of 12 factor is to define a reasonable interface for your application. The environment doesn't need to worry about providing interfaces to logging services or collecting files from a custom directory, or making sure the application isn't going to fill the disk with log output - if the app is 12 factor, the only thing the environment needs to do is collect stdout. As a 12 factor app, write such that what you put on stdout is useful for that purpose. As a system hosting 12 factor apps, collect stdout and put it somewhere useful. As a developer of a 12 factor app, when you want to see your log output, go wherever the environment puts it and look there. That's a useful contract that works at scale. Not sure why you think it doesn't.