# OpenVZ container driver

The OpenVZ driver for libvirt allows use and management of container based virtualization on a Linux host OS. Prior to using the OpenVZ driver, the OpenVZ enabled kernel must be installed & booted, and the OpenVZ userspace tools installed. The libvirt driver has been tested with OpenVZ 3.0.22, but other 3.0.x versions should also work without undue trouble.

## Connections to OpenVZ driver

The libvirt OpenVZ driver is a single-instance privileged driver, with a driver name of 'openvz'. Some example conection URIs for the libvirt driver are:

        openvz:///system                     (local access)
        openvz+unix:///system                (local access)
        openvz://example.com/system          (remote access, TLS/x509)
        openvz+tcp://example.com/system      (remote access, SASl/Kerberos)
        openvz+ssh://root@example.com/system (remote access, SSH tunnelled)

## Notes on bridged networking

Bridged networking enables a guest domain (ie container) to have its network interface connected directly to the host's physical LAN. Before this can be used there are a couple of configuration pre-requisites for the host OS.

### Host network devices

One or more of the physical devices must be attached to a bridge. The process for this varies according to the operating system in use, so for up to date notes consult the Wiki or your operating system's networking documentation. The basic idea is that the host OS should end up with a bridge device "br0" containing a physical device "eth0", or a bonding device "bond0".

### OpenVZ tools configuration

OpenVZ releases later than 3.0.23 ship with a standard network device setup script that is able to setup bridging, named `/usr/sbin/vznetaddbr`. For releases prior to 3.0.23, this script must be created manually by the host OS adminstrator. The simplest way is to just download the latest version of this script from a newer OpenVZ release, or upstream source repository. Then a generic configuration file `/etc/vz/vznetctl.conf` must be created containing

    #!/bin/bash
    EXTERNAL_SCRIPT="/usr/sbin/vznetaddbr"

The host OS is now ready to allow bridging of guest containers, which will work whether the container is started with libvirt, or OpenVZ tools.

## Example guest domain XML configuration

The current libvirt OpenVZ driver has a restriction that the domain names must match the OpenVZ container VEID, which by convention start at 100, and are incremented from there. The choice of OS template to use inside the container is determined by the `filesystem` tag, and the template source name matches the templates known to OpenVZ tools.

    <domain type='openvz' id='104'>
      <name>104</name>
      <uuid>86c12009-e591-a159-6e9f-91d18b85ef78</uuid>
      <vcpu>3</vcpu>
      <os>
        <type>exe</type>
        <init>/sbin/init</init>
      </os>
      <devices>
        <filesystem type='template'>
          <source name='fedora-9-i386-minimal'/>
          <target dir='/'/>
        </filesystem>
        <interface type='bridge'>
          <mac address='00:18:51:5b:ea:bf'/>
          <source bridge='br0'/>
          <target dev='veth101.0'/>
        </interface>
      </devices>
    </domain>