Now, my server moved to the digitalocean. I need to setup again VPN. However, digitalocean have good documentation for server setup like VPN. You can check https://www.digitalocean.com/community/articles/how-to-setup-your-own-vpn-with-pptp . It’s easy and clear. We can easily setup VPN on our Ubuntu server and only take 15 minute to setup if you know well Linux.