Proxy traffic from old to new server to allow for smooth DNS transitions

apache.cnf

# proxy traffic from original to new machine to allow for smooth DNS transfers
# Set new-www.therealserver.com up in /etc/hosts on the original machine
<VirtualHost *:80>
  ServerName www.therealservername.com
  RewriteEngine On
  RewriteRule ^(.*)$ http://new-www.therealservername.com$1 [P,L]
  ProxyPass / http://new-www.therealservername.com/
  ProxyPreserveHost On
  <Proxy *>
    Allow from all
  </Proxy>
</VirtualHost>