What does a server need to run a VPN?

Question

I have server from OVH, the HOST-64L, that has an Intel Xeon D-1520 and 64GB DDR4 ECC 2133 MHz ram. I have it configured with three 600GB SAS drives. I believe this is an overshot to sell VPN's. What are the bare minimum needs that a server might have to run decent to good VPNs? The server I have now is not cost effective as I have yet to start selling. Thanks.

Answer 1

You need to define what you mean by 'decent to good' and decide what VPN software you are using.

If you want high security then you probably want a fast CPU that has the AESNI (or similar) instruction (your Xeon D-1520 does not). If you want low latency, high throughput then you need a good network. If you are using OpenVPN then, as it is single threaded lots of cores may not be useful but you can always run multiple instances on different ports. VPN Servers are when all is said and done just routers, they don;t need much RAM.

To answer your headline question, it needs a CPU and network that is capable of the workload required everything else is likely immaterial.

Answer 2

In general this depends on what kind of VPN software you are going to use. In this case I will assume OpenVPN as this is one of the most popular ways to use a VPN. I assume that you have ordered the server for a different purpose and are trying to figure out where you can use it for. It is not smart to first buy something that may not work out best.

To understand what hardware is required, you need to understand the software. A VPN does not require fast disks nor a high amount of storage. However, since a VPN is mostly encrypting data, you will need a decent CPU for encryption. Best would be a CPU with support for AES encryption. The server you currently have does support AES-NI and is suitable for hardware accelerated performance. OpenVPN can use this in order to optimise the throughput if AES encryption is enabled. However, the Xeon D lines are not the fastest CPUs available but it might be a good start.

How much capacity is needed is hard to tell and mostly a secret of each VPN company. If you want more capacity you simply need a more powerful CPU. In general, the more powerful the CPU, the more capacity it can handle. However, be careful and do limit the transfer rate per client. Also take some security measures to prevent abuse, such as limited amount of e-mails that can be send per minute.

I know that lots of small VPN companies usually rent a VPS (Virtual Private Server) and install VPN server software on it. This does save them some buck in the beginning and you may scale the VPS more easily if you need more performance. If the VPN server is hitting its limits, they simply upgrade the CPU cores or add more VPN servers to compensate. This also allows you to use the same budget to have more servers over several locations.