Ask HN: Principle of Least Privilege in Rails?

Hello, I'm still flushing out a migration from php to rails and was wondering about security practice of "principle of least privilege"

In php we ran apache under apache:www, we had a deploy user called deploy. All files/folders would be deploy:deploy for ownership. Whenever an application required write access to a file or folder (like logs, user uploads, caches, etc) we would `chmod g+w some_file_or_dir` and `chgrp www some_file_or_dir` The idea being you strictly control what is written should someone exploit apache/your web app.

I was able to set this up with Passenger by specifying `PassengerDefaultUser apache` and `PassengerDefaultGroup www` after disabling user switching. Again we are not hosting other agency's, all apps are owned by us hence our single deploy user. I also set /var/www/.passenger folder to be owned by www. Finally for all the rails apps I had to set the group to www for the logs folder. If there were some file uploads I set www to that folder as well.

I'm a developer first and foremost and don't claim to be a system admin, this was just a practice they beat into me over the years of php dev.

Does anyone do a setup similar to this? Would this have limited the recent YAML exploit?

Is this a valid practice or being overly concerned, thoughts?

I have not looked into this for unicorn based deployments like rbenv/37signals suggests and I believe github/twitter also use unicorn. I started with passenger since that was a similar setup to php/apache vs nginx/unicorn