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iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

References (network)

Toolstacks (a.k.a toolkits and toolboxes)

There are several toolstacks available for the personal or scripted administration of Xen resources.

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Toolstacks (a.k.a toolkits and toolboxes)

There are several toolstacks available for the personal or scripted administration of Xen resources.

Primary reference: http://wiki.xen.org/wiki/Choice_of_Toolstacks

Apparently, once a toolstack has been chosen, it is not easy to change.  From Debian 7 Wheezy's /etc/default/xen (where the chosen toolstack is configured):

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  1. The shell runs /usr/sbin/xm which is a symlink to /usr/lib/xen-common/bin/xen-toolstack-wrapper
  2. /usr/lib/xen-common/bin/xen-toolstack-wrapper:
    1. Sources /usr/lib/xen-common/bin/xen-toolstack to set TOOLSTACK to /usr/lib/xen-4.1/bin/xl
    2. Sources /usr/lib/xen-common/bin/xen-dir to set dir to /usr/lib/xen-4.1
    3. Sources /usr/lib/xen-common/bin/xen-version to set VERSION to 4.1
      1. /usr/lib/xen-common/bin/xen-version gets Xen version info from /sys/hypervisor/version/*
    4. Sets PATH to /usr/lib/xen-4.1/bin
    5. Sources /etc/default/xen to set TOOLSTACK to xl (would fall back to hardcoded default otherwise)
    6. Sets TOOLSTACK to /usr/lib/xen-4.1/bin/xl
    7. Generates message "ERROR: A different toolstack (xl) have been selected!"

Creating DomUs

xen-create-image

xen-create-image is part of the xen-tools package.  TODO: does it build the image from Dom0's OS?  If so we might prefer not to use it because Dom0 was installed from the Hetzner Debian image and an uncustomised Debian may be preferable.

Using Debian Installer

Allows installation of an uncustomised Debian.

Reference: http://wiki.xenproject.org/wiki/Debian_Guest_Installation_Using_Debian_Installer

Troubleshooting

TODO: integrate the next para.

A quick note, there are actually 3 modes, not two when it comes to the drivers in use:

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Maintaining Debian DomUs

This is listed before "Creating Debian DomUs" because a newly created Debian should be updated during installation.

Installing apt-cacher on Dom0 will save bandwidth and speed maintenance (and require significant time cleaning broken cache files).

Creating Debian DomUs

debootstrap

TODO: determine if it creates a new installation based on the existing installation (that would not be desirable if we want to have all our Debians as standard and the Dom0 is a Hetzner customised Debian).

TODO: determine whether debootstrap's single repo limitation would be significant for us.

References:

Debian installer

Is the standard Debian installation method; it supports installation of standard Debian as a Xen PV.

Note: If we use either of the Debian installer methods, pre-seeding would be advantageous both for creating installations that differ only as intended and – more importantly – to accelerate re-installation during disaster recovery.  This might be very useful for all Debian and ubuntu installations, not just DomUs.  Reference: http://www.debian.org/releases/stable/amd64/apb.html.en.  Actually FAI (http://fai-project.org/ and BLUE-1325) is the way to go but it will take too long to familiarise with it.

References:

Netboot

http://www.debian.org/releases/stable/amd64/ch04s05.html.en

.iso image

xen-create-image (from xen-tools)

xen-create-image is part of the xen-tools package.  TODO: does it build the image from Dom0's OS?  If so we might prefer not to use it because Dom0 was installed from the Hetzner Debian image and an uncustomised Debian may be preferable.

 

 

Troubleshooting

TODO: integrate the next para.

A quick note, there are actually 3 modes, not two when it comes to the drivers in use:

  • HVM: unmodified kernel and drivers using software emulated devices
  • PV-HVM: unmodified kernel with paravirtualized (Xen specific) disk and network drivers
  • PV: modified kernel and drivers

For a Xen guest/DomU you can do a very basic uname and lsmod with a grep to list the modules in use:

uname -a lsmod | grep xen

If uname -a lists a kernel with the string "xen" in it, then you have a modified kernel and it's likely a PV guest, and you will see output from the lsmod command to confirm it. If you have output from the grep on lsmod but no sign of a modified kernel then you are PV-HVM. Without any sign of either, it's a straight HVM.

Note: Generally you can do more with VMs that have the PV tools installed, so that can be quite an obvious pointer, however you can fake the presence of the PV tools to allow suspend/resume etc. so you cannot rely on that in general.

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  • Domain  a Xen VM.
  • dom0  The Xen domain/VM used a) to control the hypervisor b) as the primary interface to the hardware.
  • domu*  Unprivileged Xen domains/VMs
  • Enlightened guest  An OS designed/modified for use in a domain/VM.
  • Full virtualisation  A domain/VM providing full emulation of physical hardware.  The OS can be the same as runs on real hardware.
  • Guest domain  Same as domu*.
  • Hardware Virtual Machine (HVM)  Same as full virtualisation.
  • Hypervisor a software system that allows the execution of multiple virtual guest operating systems simultaneously on a single physical machine. Xen's hypervisor is Type 1 or “bare-metal”, meaning it runs on the physical machine as opposed to within an operating system.
  • HVM  Hardware Virtual Machine.
  • Para-virtualizationvirtualisation  uses modified guest operating systems a.k.a. enlightened guests. They don’t require virtual hardware devices, instead they make special calls to the hypervisor that allow them to access CPUs, storage and network resources.  Better performance that full virtualisation.
  • PV  para-virtualisation.
  • Virtual Machine Monitor (VMM)  Same as hypervisor.
  • Xen Store  A database of information shared by the hypervisor, the kernels, the drivers and the xen daemon.  The memory for Xen Store is provided by Dom0.  In Dom0 (and in enlightened guests?) it can be accessed via /proc/xen/xenbus/

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  • /etc/default/xend
  • /etc/default/xendomains
  • /etc/init.d/xen
  • /etc/init.d/xendomains
  • /etc/xen/scripts/*
  • /etc/xen/xend-config.sxp
  • /etc/xen/xend-pci-permissive.sxp
  • /etc/xen/xend-pci-quirks.sxp
  • /etc/xen/xl.conf
  • /lib/udev/rules.d/xen-backend.rules
  • /lib/udev/rules.d/xend.rules
  • /usr/lib/xen-common/bin/*
  • /usr/sbin/cpuperf-perfcntr
  • /usr/sbin/cpuperf-xen
  • /usr/sbin/xe
  • /usr/sbin/xenperf
  • /usr/sbin/xenpm
  • /usr/sbin/xentop
  • /usr/sbin/xentrace
  • /usr/sbin/xentrace_format
  • /usr/sbin/xentrace_setmask
  • /usr/sbin/xentrace_setsize
  • /usr/sbin/xl
  • /usr/sbin/xentopxm
  • /usr/sbin/xentrace
  • /usr/sbin/xentrace_format
  • /usr/sbin/xentrace_setmask
  • /usr/sbin/xentrace_setsize
  • /usr/sbin/xl
  • /usr/sbin/xm
  • /usr/share/xen-utils-common/default.xen

xenstore-utils

Provides (all in /usr/sbin):

  • xenstore-ls
  • xenstore-write
  • xenstore-exists
  • xenstore-rm
  • xenstore-chmod
  • xenstore-watch
  • xenstore-list
  • xenstore-read

References

Documentation

xenstore-utils

Provides (all in /usr/sbin):

  • xenstore-ls
  • xenstore-write
  • xenstore-exists
  • xenstore-rm
  • xenstore-chmod
  • xenstore-watch
  • xenstore-list
  • xenstore-read

References

General references are listed here.  Specific references are listed in the sections they apply to above.

Introductory

Entry points

These are entry points to references.

Setup logs

 

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