You are using apache with proxy module, but when you try to get your page, you get a error 500 ?
Check your apache error log, if you get this :

proxy: No protocol handler was valid for the URL /. If you are using a DSO version of mod_proxy, make sure the proxy submodules are included in the configuration using LoadModule.

You need to enable proxy module :

a2enmod proxy_http
a2enmod proxy

And restart you apache server.