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Isolating websites on a single machine from each other the underlying OS (i.e. without using a bare-metal hypervisor such as ESX) can be achieved using "container" technologies, such as:

  • chroot
  • OpenVZ
  • KVM
  • Xen
  • FreeBSD jails
  • Solaris zones
  • LXC (Linux containers)
  • (... more here ...)

What are the pros, cons and other important details of each?

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The link from Warner is a good starting point :)

If you only do linux:

OpenVZ

  • Requires a kernel patch
  • Not really supported with latest distros (e.g. Ubuntu Lucid)

LXC

Fact is these are more luxury chroot options: you don't really have independent VM's (Virtual Machines) with their own resources (i.e. they all use the same disk).

The "disadvantage" of freeBSD jails and Solaris zones are that they are more or less proprietary and have a smaller user base. Also with jails and zones you don't have real independent VM's.

If you want complete virtualization and have money to spare:

VMware's vSphere

would be my choice. With full licencing you get nice options like:

  • Thin provisiong (only diskspace is claimed you really use)
  • HA (high availability: like moving VM's if the underlying hardware falls apart)
  • vMotion (move VM's on the fly)
  • DRS (distributed resource scheduler)
  • DPM (distributed power management)
  • Distributed switch (centralizes switch config).

In the end the licensing cost will weight up to reduced costs on setting up server, hardware and power consumption, depending how much you virtualize of course. Big drawback in my opinion is vSphere depends on an administrative windows client (running vCenter).

Xen

I believe you still use templates to setup a VM (Virtual Machine) but with VMware it's quite easy to setup a kickstart server and PXE-boot/kickstart new VM's.

To be short: it all depends on your needs :)

  • P.S: I did not mention "cloud solutions" (like Amazon's EC2 or Ubuntu clouds), no experience with it yet.. – Oscar Jul 27 '10 at 17:25
  • I take umbrage to your description of Jails and Zones as 'proprietary'. Jails is BSD-licensed, and Zones is open-source. Both are well-documented. Their user base is smaller. – Luke has no name Jul 27 '10 at 17:55
  • Fair enough, That's why I said "more or less". But zones outside Solaris are rare. But I agree you can say the same of LXC outside of Linux :). – Oscar Jul 27 '10 at 23:26
  • I wouldn't write off Xen or KVM versus VMware. You simply have to be more technically competent to utilize them on the same level. – Warner Jul 28 '10 at 17:47
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chroot

Pros:

  • Traditionally used as isolation container
  • Same OS so no virtualisation overhead
  • Lots of documentation exists, e.g. chroot for apache

Cons:

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