Implementation of shared hosting. How to isolate the user from the system?

Question

Network administration

Everyone knows shared hosting. For the sake of pleasure, I want to write my own billing panel with resource management.
Who knows what - share:
1) Are shareds relevant at all?
2) How to isolate a user? On the example of PHP-FPM + NGINX + MySQL + SFTP?
3) In which direction to dig, what to study?
Or maybe it's even easier to implement miniVPS with the help of visualization and thereby limit yourself and give "freedom" diluted with pre-installed panels like webmin or vesta?

Answer 1

Look at CloudLinux - there it is and much more needed for Wirth. hosting