Usually when you create a VPS on your virtualization platform you give it a public IPv4 address but with RIPE, ARIN and other NCCs running out datacenters are shooting up their prices and we need to find another way. IPv4 NAT ports.

What is a VPS?

In essence a VPS is a virtual computer/server running inside the main "dedicated" server. It has it's own shell and it's allocated it's own resources, it thinks it's a real server. If you know what a virtual machine is, a VPS is just a fancy name for that.

What is OpenVZ?

OpenVZ is a hypervisor, it allows you to run "containers" which are VPSs which share the same kernel as the host (dedicated server). It's one of the most lightweight, little-overhead hypervisors out there and is commercially used by many providers around the world.

What is an IPv4 NAT port?

This is simply a port on the host node with the host's IPv4 address which is forwarded to the OpenVZ guest and the client can therefore access a service (or range of) e.g SSH from the outside world without having a dedicated IPv4 address.

Giving internet access to NAT'd OpenVZ containers

First you need to create a OpenVZ container, this is fairly simple and there are plenty of guides covering this (e.g here) so I won't go over it here.

After that you have to assign the container a private IPv4 address (e.g 192.168.0.1):

vzctl set 101 --ipadd 192.168.0.1 --save

In /etc/modprobe.d/openvz.conf change options ip_conntrack ip_conntrack_disable_ve0=1 to options ip_conntrack ip_conntrack_disable_ve0=0. Then you need to make sure the containers can access the internet from the outside: iptables -t nat -A POSTROUTING -o eth0 -j SNAT --to public_server_ip

You need to replace public_server_ip with a public IPv4 address on your "dedicated" server. This is the IPv4 address that the clients on the containers will use to connect to their services on their containers.

Forwarding ports to containers

To allow outside users to access ports on containers you will need to forward them with the following command:

iptables -t nat -A PREROUTING -p tcp -d public_server_ip --dport PORT -i eth0 -j DNAT --to-destination 192.168.0.1:CLIENTPORT

You need to set public_server_ip with the same IPv4 address you set above. You need to replace PORT with the port you want outside users to use and CLIENTPORT to the port of the service inside the container. Once you've done this, everything will work smoothly.

How can you use this?

An example is what I'm currently working on Defined Code Hosting where we provide extremely cheap VPSs £4/year for 64MB RAM and £8/year for 128MB RAM. You can see these plans here.

Contact

If you need any help, you can find me on twitter @Will3942 and you can comment on this article at Hacker News here or you can email me: will@will3942.com