I know it’s a noobish question?
Are they the same?
AFAK workers are for Apache and child processes are for PHP-FPM?
Thanks in advance,
They are both child processes forked from a parent process, yes. The difference between mod_php and something like PHP-FPM is that mod_php embeds itself as a shared object inside of the apache httpd child worker processes and thus those processes serve as both a web serer process as well as a php process. PHP-FPM, on the other hand, operates outside of the web server as its own Fork-Process-Manager and only communicates with the web server over FastCGI. These are both considered prefork-mpms, however. Also, you can still use FastCGI in apache httpd. So that the child workers are not a part of the web server workers. So this isn’t exclusive to nginx.
Here’s a visual of how the two prefork styles might look:
Using PHP-FPM and Nginx
Using mod_php and Apache httpd