Just a quick note on installing mod_proxy_html for Apache in CentOS. I have seen several methods, but, assuming you have the EPEL repos added to Yum, it is pretty much a one-liner:
yum install mod_proxy_html
Once installed, it is just a matter of adding the following line to your httpd.conf file and restarting Apache:
LoadModule proxy_html_module modules/mod_proxy_html.so
This will allow you to use the ProxyHTMLURLMap directive. To learn more, check out Apachetutor.org’s tutorial.