How-to understand what VPS is

[goldigger]

It appears many people find it hard to understand what VPS is and how it works, so I just thought I'd make a small effort to explain a littlebit.

What does VPS mean?
Virtual Private Server

What is such a Virtual Server?
Basically VPS is all about running multiple Virtual Servers within one physical server.

What does Private refer to?
Each VPS gets its own portion of resources, which are usually guaranteed to be available to that particular VPS. For instance, the host server may have 8GB of ram, and 256mb (for instance) could be guaranteed to be available to a VPS. That would mean that regardless of what other VPS's on the same server use, that amount of RAM will be available to the VPS.

Also very important: each VPS runs completely independent of eachother. Each VPS has its own filesystem so a VPS can't see any of the data of another VPS. Also each VPS has it's own server load, can run its own Operating System, can be rebooted individually, and so on. Basically by the end user it can be treated as a dedicated server.

So does a VPS also have its own kernel?
Usually not, but it depends on the technology that the host uses.

Are VPS's truly 100% isolated from eachother, so no matter what happens they can not cause trouble to eachother?
Under normal circumstances, yes. However in extreme scenarios, VPS's can trouble eachother. For instance if the host server has a 100mbit uplink, and one VPS gets a 100mbit DDoS attack, then it makes sense that all other VPS's on the same server are also affected by it. It's up to the host to ensure maximum reliability by monitoring everything closely.

I mentioned VPS's on the same host server can each run a different Operating System. So could one VPS on the server run Windows, and another one Linux?
No, that's not possible. It is however possible to run different Linux distributions on a Linux VPS server. For instance one VPS could be running Red Hat Enterprise, and another one could be running Debian.

Is it possible to run anything on a VPS that would run on a dedicated server?
As long as it doesn't require kernel modifications, yes. (note: some technologies do support kernel modifications - that's not something I specialize in though)


For everyone who still has trouble understanding what VPS is, I thought of a nice example:

You could compare VPS technology to a block of apartments. The block has one roof, but under that roof there are multiple apartments. Each apartment has its own kitchen, living room, etc, so it can operate individually. Everyone goes in and out through the same door of the building though (VPS: traffic all goes through one network port). And I'm sure you can think of every other similarity.