Currently I run single tomcat with single WAR application on port 80. The domain name www.foo.org is pointed to this server ip.
What is the procedure of ad
Usually you have a tomcat (or other application server) on port different from 80 (like 8080 or 7001 or anything you want). After that you put a web server (like apache http server) on port 80 and configure one or many connector to point to different port on different application server with different address.
For Apache http + tomcat you can take a look at this link:
http://tomcat.apache.org/connectors-doc/webserver_howto/apache.html