Big News [April 24th, 2012]: I’ve launched Wordfence to permanently fix your WordPress site’s security issues. Click here to learn more.

In web server admin parlance, a VPS is a Virtual Private Server and a VHost is a virtually hosted website. There were a few questions regarding security on VPS’s and VHosts in my previous post on “Seven ways I could hack into your WordPress website“, so I thought I’d clarify what the difference is between WordPress hosted on a Virtual Private Server (VPS) vs WordPress on a Virtual Host (VHost) and what the security implications are of each configuration.

A Virtually Hosted Website (VHost)

In the early days of the web, you would have a single physical machine running a single operating system running a single web server. That web server would serve up a single website.

HTTP 1.0 introduced the optional “Host:” header and HTTP 1.1 made it mandatory with any web request that a browser sends. The effect of this is that when a web browser sends a request to any web server, it lets the server know which website it wants to see. Because web servers know what website a browser expects, they can now host an unlimited number of websites. This is called virtual hosting.

When you have a virtually hosted website, you are sharing a single server and operating system with many other websites. Your files and the files of other websites are stored on the same operating system. You all share the same web server and the server chooses which of your websites it needs to serve based on what a web browser requests when it connects to that web server.

Usually on a virtually hosted website, you won’t have access to other website files and they won’t have access to yours. This is usually done by giving you a unique username that you use to sign in and your username only has permissions to view your files.

A Virtual Private Server (VPS)

A VPS is a little different. Normally when you install any operating system, you install it directly on a machine like a server or workstation. With a VPS, you first install a base operating system like Windows or Linux. Then you install a virtual machine hosting platform called a Hypervisor. Examples of Hypervisor’s are VMWare and Xen.

Within the Hypervisor you can then install multiple virtual machines. These pretend to be physical hardware and when you boot them up you get a BIOS message similar to when you boot up a physical machine.

Within these virtual machines you can then install an operating system like Linux or Windows. Using this config you can have potentially hundreds of virtual machines running on a single physical machine.

So to summarize, you have a physical machine running an operating which runs a hypervisor which runs multiple virtual machines and each virtual machine runs its own operating system. Within these operating systems you run your own web server, have the files for your website and do anything else you feel like doing. It’s impossible for someone on another virtual machine to access your virtual machine.

Linode is one of the most popular virtual machine hosting providers and they use the Xen Hypervisor to host Linux virtual machines.

So which is more secure?

By now you’ve probably already figured it out: Running your own virtual machine that is completely segmented from everyone else is usually the more secure option. Here are a few reasons why:

1. If your web host messed up the machine configuration or permissions, then other users may be able to access your files.
2. If another user’s WordPress installation gets hacked, it may be possible for the hacker to gain read or in rare cases read and write access to your files.

Another thing I like about having a VPS instead of a VHost is that you have your own IP address. On the Internet, IP addresses can get blacklisted, particularly if you’re sending email. If your web application sends email e.g. if you’re using the WordPress “Subscribe to Comments” plugin, then your emails may be flagged as spam if another user on the same server is sending a lot of spam.

With a VPS you have your own IP address, so as long as the IP address wasn’t already black-listed when you got it from your web host (I’ve seen it happen) then only you are responsible for how that IP address is perceived on the Net.

In conclusion: While VPS’s tend to cost slightly more (about $20/month from Linode), they are well worth the extra cost when it comes to protecting your website and your reputation. As always please post any questions in the comments and I’ll either answer them directly or in a future post.

Caveat: I have generalized greatly when it comes to VPS and VHost configurations. There are many variants including Type I and Type II Hypervisors, shared hosting where a single OS hosts one web server instance per website and many more. I’ve described two common VPS and VHost configs above for illustrative purposes, however the VPS config I describe is probably the most common configuration used by VPS providers.