|
| |
A virtual private server (VPS, also referred to as Virtual Dedicated Server
or VDS) is a method of partitioning a physical server computer into multiple
servers that each has the appearance and capabilities of running on its own
dedicated machine. Each virtual server can run its own full-fledged operating
system, and each server can be independently rebooted.
The practice of partitioning a single server so that it appears as multiple
servers has long been common practice in mainframe computers, but has seen a
resurgence lately with the development of virtualization software and
technologies for other architectures.
Overview
This short section requires expansion.
The physical server boots normally. It then runs a program that boots each
virtual server within a virtualization environment (similar to an emulator). The
virtual servers have no direct access to hardware and are usually booted from a
disk image.
There are 2 kinds of virtualizations: software based and hardware based. In a
software based virtualization environment, the virtual machines share the same
kernel and actually require the main node's resources. This kind of
virtualization normally has many benefits in a web hosting environment because
of quota incrementing and decrementing in real time with no need to restart the
node. The main examples are Virtuozzo (a product of swsoft.com), HyperVM (a
product of lxlabs.com), and openvz which is the core kernel of both virtuozzo
and hypervm.
In a hardware based virtualization, the virtualization mechanism partitions the
real hardware resources and no burst and/or realtime quota modification is
possible. The limits are hard and only modified after a restart. This kind of
environment is more secure and is useful in enterprise/commercial usages.
Examples include Microsoft Virtual Server, VMWare, and Xen.
Uses
Virtual private servers bridge the gap between shared web hosting services and
dedicated hosting services, giving independence from other customers of the VPS
service in software terms but at less cost than a physical dedicated server. As
a VPS runs its own copy of its operating system, customers have superuser-level
access to the machine, and can install almost any software that runs on the OS.
Certain software does not run well in a virtualized environment, including
firewalls, anti-virus clients, and indeed virtualizers themselves; some VPS
providers place further restrictions, but they are generally lax compared to
those in shared hosting environments. Due to the number of virtualization
clients typically run on a single machine, a VPS generally has limited processor
time, RAM, and disk space.
Due to their isolated nature, VPSes have become common sandboxes for
possibly-insecure public services or update testing. For example, a single
physical server might have two virtual private servers running: one hosting the
production-level (live) website, and a second which houses a copy of it. When
updates to crucial parts of software need to be made, they can be tested in the
second VPS, allowing for detailed testing to be conducted without requiring
several physical servers.
Virtual private servers are also sometimes employed as honeypots, allowing a
machine to deliberately run software with known security flaws without
endangering the rest of the server. Multiple honeypots can be quickly set up via
VPSes in this fashion.
Virtual private servers are often used by aggressive search engine marketers and
web spammers as well.[
| |
|
