Mods Required for apache proxy pass to be enabled.

Following are the list of modules which are required to enable proxy pass in apache2 (i.e. from apache2 to tomcat7)

sudo a2enmod proxy
sudo a2enmod proxy_connect
sudo a2enmod proxy_http

sudo a2enmod rewrite

Configuration in the apache side.

proxypass / http://localhost:8080/
proxypassreverse / http://localhost:8080/