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
andlsmod
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 thelsmod
command to confirm it. If you have output from the grep onlsmod
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.
Introduction
Xen is Blue Light's standard virtualisation solution, decided in BLUE-1192
Introduction to Xen: http://wiki.xenproject.org/wiki/Xen_Beginners_Guide#What_is_this_Xen_Project_software_all_about.3F
Installation (host/dom0)
TODO: is xen-docs useful (probably not; installed hoping for an xl man page)?
aptitude install xen-docs-4.1 xen-linux-system
Adjust grub so the default boot item is Xen (ref: https://xen-orchestra.com/cant-find-hypervisor-information-in-sysfs/)
dpkg-divert --divert /etc/grub.d/08_linux_xen --rename /etc/grub.d/20_linux_xen
update-grub
shutdown -r now
Test: does the xen list
command show that the current system is Domain-0?
Storage
The recommended way to provide storage for a DomU is by an LVM on Dom0 which the DomU uses as a virtual HDD.
Reference: http://wiki.xenproject.org/wiki/Storage_options
Networking
Choice (TODO: can be mixed?):
- Bridged Each DomU* OS is connected to the LAN
- Routed Dom0 is a router between the LAN and the DomU* network interfaces
- NATted Dom0 is a NATting router between the LAN and the DomU* network interfaces
Interface names:
- peth* The physical ethernet interfaces in a Xen bridge, connected to the LAN
- vif* The virtual interfaces in a Xen bridge, connected to the DomUs
- veth* TBC
- xenbr* A Xen bridge
Bridged
Dom0's eth0 gets the bridge's address, broadcast, netmask and gateway settings (assuming the bridge config includes bridge_ports eth0
).
Diagram from http://wiki.xenproject.org/wiki/Xen_Networking#ASCII_Art_Examples_of_Xen_Networking_Topologies:
LAN0 LAN1 | | +-----+-----------------------------------------------------+-----+ | | | | | +---+-------------------------+ +-------------------------+---+ | | | | | | | | | | | eth0 | | eth1 | | | | | | | | | | xenbr0 vif1.0 vif2.0 | | vif1.1 vif2.1 xenbr1 | | | | | \ | | / | | | | +---^------------+---------\--+ +--/---------+------------^---+ | | | | \ / | | | | | +------+-------------X-------------+------+ | | | | | | / \ | | | | | | | +----+---------/--+ +--\---------+----+ | | | | | | | | / | | \ | | | | | | | | | eth0 eth1 | | eth0 eth1 | | | | | | | | | | | | | | | | | | | +-+-+ | | +-+-+ +-+-+ | | +-+-+ +-+-+ | | +-+-+ | | | | | | | | | | | | | | | | | | | | | | www ssh | | www ssh ftp pop | | www ssh ftp pop | | ftp pop | | | | | | | | | | Domain0 | | Domain1 | | Domain2 | | Domain0 | +-----------+ +-----------------+ +-----------------+ +-----------+
Useful commands:
brctl show
Routed
Note: routing may be used with NATted.
When routing is used, need:
net.ipv4.ip_forward = 1
net.ipv4.conf.eth0.proxy_arp = 1
To make these settings permanent, ensure they are present in /etc/sysctl.conf
NATted
Note: NATted may be used with routing.
When NAT is used, need:
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
A cunning plan?
Maybe we can do what we want (as on blav; some VMs with public IPs, most with NATted non-routable IPs) without a bridge; configure the physical interface with all the public IPs and use IPTABLES to forward traffic sent to notionally the VM's public IPs to the VM's non-routable IPs. For each VM adressable by public IP:
iptables -t nat -A PREROUTING -i eth0 -d PUBLICIP -j DNAT --to-destination INTERNALIP
For NATting:
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
References (networking)
- Network Configuration Examples (Xen 4.1+): http://wiki.xenproject.org/wiki/Network_Configuration_Examples_%28Xen_4.1%2B%29
- Ethernet Bridge + netfilter Howto (2005 but has a boot script example): http://www.tldp.org/HOWTO/Ethernet-Bridge-netfilter-HOWTO.html
- Network Configuration Examples (Xen WIKI): http://wiki.xen.org/wiki/Host_Configuration/Networking
- Bridging Network Connections (Debian WIKI): https://wiki.debian.org/BridgeNetworkConnections
Toolstacks (a.k.a toolkits and toolboxes)
A toolstack is a set of user-space tools used for adminstering Xen.
Several toolstacks are available for the interactive 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):
# Attention: You need to reboot after changing this!
libvirt and virsh
libvirt is a library for managing KVM, OpenVZ, VMware, VirtualBox, Xen and others. For Xen, it is the least feature-complete of all the toolstacks.
virsh is a user/script shell to interface with libvirt. References: http://libvirt.org/virshcmdref.html
xapi and xe
The most feature-complete of all the toolstacks.
xend and xm
Deprecated since Xen 4.1 but the default in Xen 4.1 as packaged for Debian. Will be removed from Xen 4.2.
xend comprises:
- xm command
xend-config.sxp config file format
- xmdomain.cfg config file format
xl
Strategic since Xen 4.1.
Designed to be command line compatible with xend. TODO: what does this mean? man -k xend lists the config file format xend-config.sxp. It may mean command line compatible with xm; many of the xl commands take similar arguments to xm.
Unlike xm, xl does not do dom0 network configuration; standard OS tools must be used.
For help (not --help or -h): xl help
In case there is no local xl man page: http://xenbits.xen.org/docs/unstable/man/xl.1.html and (Xen 4.2) http://manpages.ubuntu.com/manpages/raring/en/man1/xl.1.html
Toolstack library
Libxenlight (libxl)
The strategic Xen toolstack library, designed to hide xenstore, libxenctrl, and libxenguest from higher levels.
Toolstack configuration
Debian 7 Wheezy
The Xen toolstack on Debian 7 Wheezy is configurable.
On blav2, we had explicitly configured using xl:
root@SON-OF-blav.bluelightav:~# diff /etc/default/xen{.org,}
7c7 < TOOLSTACK=
--- > TOOLSTACK=xl
When root runs command xl
:
- The shell runs /usr/sbin/xl which is a symlink to /usr/lib/xen-common/bin/xen-toolstack-wrapper
- /usr/lib/xen-common/bin/xen-toolstack-wrapper:
- Sources /usr/lib/xen-common/bin/xen-toolstack to set TOOLSTACK to /usr/lib/xen-4.1/bin/xl
- Sources /usr/lib/xen-common/bin/xen-dir to set dir to /usr/lib/xen-4.1
- Sources /usr/lib/xen-common/bin/xen-version to set VERSION to 4.1
- /usr/lib/xen-common/bin/xen-version gets Xen version info from /sys/hypervisor/version/*
- Sets PATH to /usr/lib/xen-4.1/bin
- Sources /etc/default/xen to set TOOLSTACK to xl (would fall back to hardcoded default otherwise)
- Sets TOOLSTACK to /usr/lib/xen-4.1/bin/xl
exec
s /usr/lib/xen-4.1/bin/xl
When root runs command xm
(does not work):
- The shell runs /usr/sbin/xm which is a symlink to /usr/lib/xen-common/bin/xen-toolstack-wrapper
- /usr/lib/xen-common/bin/xen-toolstack-wrapper:
- Sources /usr/lib/xen-common/bin/xen-toolstack to set TOOLSTACK to /usr/lib/xen-4.1/bin/xl
- Sources /usr/lib/xen-common/bin/xen-dir to set dir to /usr/lib/xen-4.1
- Sources /usr/lib/xen-common/bin/xen-version to set VERSION to 4.1
- /usr/lib/xen-common/bin/xen-version gets Xen version info from /sys/hypervisor/version/*
- Sets PATH to /usr/lib/xen-4.1/bin
- Sources /etc/default/xen to set TOOLSTACK to xl (would fall back to hardcoded default otherwise)
- Sets TOOLSTACK to /usr/lib/xen-4.1/bin/xl
- Generates message "ERROR: A different toolstack (xl) have been selected!"
DomU configuration
Each DomU (the VM itself, not its OS etc.) is configured by a file in /etc/xen.
Maintaining Debian in 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).
Installing Debian in DomUs
debootstrap
Installs into a chroot. Can use only one repository (which may be a local cache).
References:
- Debian WIKI: https://wiki.debian.org/Debootstrap
Installing new Debian systems with debootstrap (2006): http://www.debian-administration.org/article/426/Installing_new_Debian_systems_with_debootstrap
Installing Debian GNU/Linux from a Unix/Linux System: http://www.debian.org/releases/stable/amd64/apds03.html.en
Debian installer
"Debian installer" is the standard Debian installation system; it supports installation of standard Debian as a Xen PV.
Pre-seeding
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.
Even pre-seeding is non-trivial so decided not to delay the first installation by using it.
References:
- http://wiki.xenproject.org/wiki/Debian_Guest_Installation_Using_Debian_Installer
- Debian GNU/Linux Installation Guide (Wheezy 64-bit version): http://www.debian.org/releases/stable/amd64/
Netboot
http://www.debian.org/releases/stable/amd64/ch04s05.html.en
.iso image
Installing from a .iso image is the method we are most familiar with so a good choice, at least for the first DomUs.
Installation method decision
24 July 2014
Decided to install from a .iso rather than any of the other choices because:
- We are already familiar with it
- Having no integration into the Xen architecture, we will learn more about Xen during the domU process.
xen-create-image (from xen-tools)
xen-create-image is part of the xen-tools package.
When creating Debian systems it uses debbootsrap (described above).
Monitoring and controlling DomUs
Troubleshooting
TODO: integrate the next para.
TODO: integrate the next text
So basically bootloader (grub/pygrub or xen pv bootloader) sets up the kernel and initrd in memory, and boots the kernel. Kernel then extracts the initrd from the memory, and executes the script in the initrd. The script then loads the necessary drivers for *that* particular server hardware or a virtual machine to access the actual root disk, and then the script mounts the root disk so the actual Linux distribution can be started from the real root disk. So the initrd image you use must be suitable for the Xen domU and load the required kernel modules (possibly xenblk) and set up the xen xvd-disks!
References
Files and directories
File or directory | Usage | Notes |
---|---|---|
/etc/default/xen | ||
/etc/default/xend | ||
/etc/default/xendomains | ||
/etc/xen/ | Configuration | |
/etc/xen/scripts/ | ? | |
/etc/xen/scripts/vif-nat |
Glossary
- 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-virtualisation 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/
Technical
TODO; move Xen notes from the Online.net server page to here.
Architecture
Very little information found on the 'net about Xen architecture. This diagram is from http://libvirt.org/architecture.html
TODO: mine http://wiki.xen.org/wiki/XenIntro for more information.
Primary reference (no Xen 4.x equivalent found): http://wiki.xen.org/wiki/XenIntro
Debian packages
libxen-4.1
Includes /usr/lib/libxenctrl-4.1.so and /usr/lib/libxenguest-4.1.so
libxenstore3.0
Includes /usr/lib/libxenstore.so.3.0.0 and /usr/lib/libxenstore.so.3.0
xen-hypervisor-4.1-amd64
Includes /boot/xen-4.1-amd64.gz
xen-linux-system-3.2.0-4-amd64
Documentation only. TODO: presumably its dependencies are crucial; list them?
xen-linux-system-amd64
Documentation only. TODO: presumably its dependencies are crucial; list them?
xen-system-amd64
Documentation only. TODO: presumably its dependencies are crucial; list them?
xen-tools
Tools that work with the xm and xl toolstacks to administer Xen config files and images.
Provides (in /usr/bin):
- xt-customize-image
- xt-create-xen-config
- xen-list-images
- xen-delete-image
- xt-install-image
- xen-create-nfs
- xen-create-image
- xt-guess-suite-and-mirror
- xen-update-image
Plus, presumably in suppport:
- /etc/xen-tools/*
- /usr/lib/xen-tools/<OS name>.d/*
xen-create-image largely automates creating domUs. Config file: /etc/xen-tools/xen-tools.conf. The --lvm
option creates a new logical volume which is available to the domU as a hard disk drive
Logs in the /var/log/xen-tools/ directory.
References
- Xen-Tools.org documentation: http://xen-tools.org/software/xen-tools/
- Xen-Tools.org FAQ: http://xen-tools.org/software/xen-tools/faq.html
- Xen Project Community Blog: Xen-Tools page: http://blog.xen.org/index.php/2012/08/31/xen-tools-a-straightforward-vm-provisioninginstallation-tool/
xen-utils-4.1
Tools to control the hypervisor from dom0.
Provides (in /usr/lib/xen-4.1/bin/):
- xentrace_setsize
- xenpm
- xen-python-path
- qemu-dm
- xsview
- xen-hvmcrash
- xentrace_setmask
- xenstored
- xentrace_format
- xenbaked
- readnotes
- xenconsoled
- xc_restore
- gtraceview
- xen-bugtool
- xen-hptool
- xentop
- xend
- xc_save
- gtracestat
- xenctx
- xenwatchdogd
- xenpaging
- pygrub
- xencons
- xen-detect
- lsevtchn
- tap-ctl
- xl
- xentrace
- xm
- xen-hvmctx
- xenconsole
- xenstore-control
- xenmon
- xenlockprof
- xen-tmem-list-parse
- xenperf
Plus, presumably in suppport:
- /usr/lib/xen-4.1/lib/
- /usr/lib/xen-4.1/boot/hvmloader
xen-utils-common
Provides:
- /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/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
General references are listed here. Specific references are listed in the sections they apply to above.
Introductory
- Wikipedia: http://en.wikipedia.org/wiki/Xen
- Debian Wiki Xen page (in draft): https://wiki.debian.org/Xen
- Xen Project Beginners Guide: wiki.xenproject.org/wiki/Xen_Beginners_Guide
- XPSU13 VIDEO: Xen for Beginners (49 min): http://www.xenproject.org/help/presentations-and-videos/video/latest/xpus13-beginners.html
Entry points
These are entry points to references.
- Xen WIKI: http://wiki.xenproject.org/wiki/Main_Page
- Xen man pages: http://wiki.xenproject.org/wiki/Xen_Man_Pages
Setup logs
- Xen On Debian Wheezy With LVM (HowtoForge. Has bridge example with fixed IP): http://www.howtoforge.com/xen-on-debian-wheezy-with-lvm
- Using Xen With LVM-Based VMs Instead Of Image-Based VMs (HowtoForge. Etch): http://www.howtoforge.com/using-xen-with-lvm-based-vms-instead-of-image-based-vms-debian-etch
- Debian Wheezy -> Jessie and set up Xen (HowtoForge): http://www.howtoforge.com/how-to-set-up-xen-4.3-on-debian-wheezy-7.0.2-and-then-upgrade-to-jessie
- Setting up XEN on a Hetzner Dedicated Server (Squeeze, xen-create-image, xm): https://gist.github.com/meskyanichi/3354956
- Routed XEN VM based on LVM (step-by-step for Hetzner DS3000. Lenny): http://wiki.summercode.com/routed_xen_vm_based_lvm_step_by_step_guide_for_hetzner_ds3000
- Xen on 4 app servers (xl, no public IPs): http://wiki.xenproject.org/wiki/Xen_on_4_app_servers
- The Debian Administrator's Handbook, Virtualisation chapter (Nice. xen-tools, xm, bridged): http://debian-handbook.info/browse/stable/sect.virtualization.html
- How to install Xen in Debian (Armen's Wiki. Has scripts for both public and private IPs for virtual machines): http://vardump.org/wiki.php/HowToInstallXenInDebianGNULinux.