I have manually configured multiple instances of Apache on CentOS 6, with virtual hosts proxying on port 80/443 to the correct Apache instance (running on alternate ports), mostly by following this guide:
The only part lacking is making a clean startup script that starts/stop Apache properly (following CentOS's policies). I eventually made my own by copying+editing
/etc/init.d/httpd, although I cannot say it's perfect. The guide above mentions that Debian and Ubuntu have support in their startup scripts to multiple instances.
So I gather that Ubuntu has support out of the box for multiple Apache instances, including scripts to setup those instances. Does CentOS have anything like that? I'm stuck using CentOS due to the control panel requiring it on this box, and unfortunately multiple instances really is required for my project.