LXC containers or extremely fast virtualization

Update: Added an hardy i386 template, mentioned the need of bridge-utils and fixed typo (s/addbr/brctl addbr/g)

This (quite long) post is about the LXC (Linux containers), an example of its usage on Karmic is provided after the introduction to contextualization.

Most of you are probably already familiar with “usual” virtualization as kvm/virtualbox/vmware/… These are now extremely fast ways to do “full” virtualization of an OS on a host running either the same OS or a completely different one.
In Ubuntu, the most widely used is probably KVM used with libvirt and virt-manager as frontend.

At Revolution Linux, we have literately hundreds of virtual machines for each of our customers and we noticed that they are all Ubuntu virtual machines running on Ubuntu hosts. Then, running them in a “full” virtualization environment adds unneeded overhead and makes resource assignment quite difficult (you can’t easily change the CPU/RAM/DISK/NIC of a running virtual machine).

So, what we are currently doing is using contextualization instead of regular virtualization.
Contextualization can (in a much simpler way) be seen as improved chroots, these “chroots” are called containers and work just like a regular virtual machine, inside them you have your own network interface, can apply disk/cpu/ram quotas and start/stop/suspend as many of them as you want.
All the quotas and restrictions can be changed on the fly without needing any restart, because it’s technically just a set of process running on the host, not a single process as with virtualization.
It also means that you can list/kill or execute a process in any of these containers, directly from the host (a container obviously can’t access another’s processes).

The technology we have been using for more then a year now has been OpenVZ (open source implementation of Virtuozo) which basically is a huge patchset on top of the Linux kernel and only exists in Ubuntu hardy (8.04 LTS).

What I’ve been looking at more recently and hope to have working correctly in Lucid (10.04 LTS) is LXC. LXC is basically the same as OpenVZ except that it’s in the upstream kernel and uses already existing kernel features such as “cgroups” for example.
LXC is also supported by libvirt although it’s not working in Karmic, that will let users play with it just like any other virtualization technology using their existing scripts and interfaces.

Here’s a quick howto to make it work on Karmic with an Ubuntu 8.04 amd64 container (I’ve had issues making Karmic to work in a container):

  • Install bridge-utils: sudo apt-get install bridge-utils
  • Install LXC from my PPA (upstream snapshot) : https://launchpad.net/~stgraber/+archive/ppa/+packages
  • Create /var/lib/lxc/: mkdir -p /var/lib/lxc/
  • amd64 template (if your computer is running Ubuntu 64bit): Get http://www.stgraber.org/download/lxc-ubuntu-8.04-amd64.tar.gz (Hardy amd64 image)
  • i386 users (if your computer is running Ubuntu 32bit): Get http://www.stgraber.org/download/lxc-ubuntu-8.04-i386.tar.gz (Hardy i386 image)
  • Uncompress it in /var/lib/lxc/ (will create an ubuntu directory containing a configuration file and a root directory)
  • Mount cgroups somewhere: sudo mkdir /dev/cgroup && mount -t cgroup none /dev/cgroup
  • Create a bridge with: sudo brctl addbr br0
  • Set an IP on the bridge: ifconfig br0 (VE will be by default)
  • Start the VE: lxc-start -d -n ubuntu
  • Enter the VE: “lxc-console -n ubuntu” or “ssh root@” (root password is “password”)

The VE (virtual environment) configuration file is in: /var/lib/lxc/ubuntu/config

Additional information can be found on:

Also, I plan to have a session about it at UDS-Lucid in Dallas

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19 Responses to LXC containers or extremely fast virtualization

  1. Pingback: State of LXC in Ubuntu 11.04 | Stéphane Graber's website

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