Comment Apache MPM Worker + FastCGI with fcgid (Score 2) 209
The mistake is trying to use mod_php with a heavy PHP application, such as a a complex Drupal site, without a reverse proxy such as Varnish or nginx.
One trick I have been using for a few years is using Apache as a threaded server, with MPM Worker, and FastCGI but with fcgid, not mod_fastcgi. Works exceptionally well. For static files, Apache is now lightweight and does not use much RAM.
For details, see my article on Apache MPM Worker with fcgid.