Setting up Openvpn between Pi and Ubuntu server
From MyWiki
This is probably good - https://www.digitalocean.com/community/tutorials/how-to-set-up-an-openvpn-server-on-ubuntu-14-04
This is probably good - https://www.digitalocean.com/community/tutorials/how-to-set-up-an-openvpn-server-on-ubuntu-14-04