The easiest way to have 2 (or more) domains point to the same Ruby on Rails app is to setup your first domain the same way you do for a normal implementation. I use Rails Machine for all my rails apps so I just follow the normal 5 minute deploying process they provide.

That sets up domain1.com. Now to setup domain2.com I ssh into my server. Navigate to my httpd conf files. Mine is located here:

>/etc/httpd/conf/apps

Then I copy my domain1.com conf file called domain1.conf and call the new one domain2.com.

I then edit this file and change any reference to domain1.com to domain2.com.

Save the file, then reset your httpd

>sudo /etc/init.d/httpd reload

and voila!