Is there a way to run Ruby on Rails app on Apache HTTPD (CentOS)?
Is this just a matter of setting up httpd.conf with VirtualHost?
Passenger is probably the easiest way to get that running. Here's a tutorial on installing Passenger on CentOS6, and here are prebuilt rpms.
Check Rails site, I think you have to use a Proxy, unless I'm misunderstanding what you mean by HTTPD. Seems like you want a simple Apache setup, Rails should be able to help.
EDIT: James answer looks perfect. Same as mine, but he has real CENTOS tutorials... I've never used CENTOS, just done this through Ubuntu.
You can run mod_rails aka Passenger or a Mongrel Cluster or Thin Cluster.
I find passenger the easiest, you can download it Here
The Steps are quite easy
sudo gem install passenger
sudo passenger-install-apache2-module
Follow instructions on screen.