Using FAI to set up XEN domains
This section provides short guidelines on how to set up XEN base systems (aka domain-0) and virtual machines (dom-U) using FAI. Henning Glawe (http://www.physik.fu-berlin.de/~glaweh/) provided many ideas and some scripts - thanks!
Apart from configuring FAI, the following things need to be considered:
- Which XEN packages should be used?
- XEN kernel images need to be built
- Find a partitioning scheme and figure out whether you want to use LVM, native partitions or files
Preparing FAI:
For the domain-0 only the kernel-image must be set correctly. As I'm using LVM for the unpriveledged domains and FAI can't do that yet, I wrote a little script to set up all of them later (it failed when I tried to do it during the FAI installation, should debug that).
The more interesting part is the preparation of unpriveledged domains. As these require no partitioning during installation a hook must be created:
partition.XENU:
[ -f $LOGDIR/our.skip.partition ] && exit 0 for our_cl in $classes; do [ $our_cl = "XENU" ] && continue [ -f $FAI/hooks/partition.$our_cl ] && exit 0 done mke2fs -j /dev/hda1 > /dev/null mkswap /dev/hda2 > /dev/null mke2fs -j /dev/hda3 > /dev/null mke2fs -j /dev/hda4 > /dev/null mke2fs -j /dev/hda5 > /dev/null cat > /tmp/fai/fstab <<EOF /dev/hda1 / ext3 defaults 0 0 /dev/hda2 none swap sw 0 0 /dev/hda3 /tmp ext3 defaults 0 0 /dev/hda4 /usr ext3 defaults 0 0 /dev/hda5 /var ext3 defaults 0 0 EOF echo "#!" > $diskvar touch $LOGDIR/skip.partition
Furthermore, a XEN-kernel for the class XENU must be configured - and FAI is prepared.
Booting XEN domains from the network
Starting from the example config provided by xen, xmexample2, I made my scripts support the following:
xm create <domainname>
starts the domain as usual,
xm create <domainname> vminstall=1
starts a FAI installation.
The configuration for my domain named boss is thus (obey spaces, this is python code...)
#============================================================================ # This script sets the parameters used when a domain is created using 'xm create'. # # "xm create vminstall=1" will (re)install the domain or # "xm create" will boot the domain # # vminstall is purely a script variable, and has no effect on the the domain # id assigned to the new domain. #============================================================================ # Define script variables here. # xm_vars is defined automatically, use xm_vars.var() to define a variable. # This function checks whether 'vminstall' has been given a value. # It is called automatically by 'xm create'. def vminstall_check(var, val): try: val = int(val) except: val = 0 if val <= 0: val = 0 return val # Define the 'vminstall' variable so that 'xm create' knows about it. xm_vars.var('vminstall', use="Reinstall domain if value > 0.", check=vminstall_check) # Check the defined variables have valid values.. xm_vars.check() kernel = "/boot/xen-linux-2.6.11.12-xen" memory = 384 name = "boss" cpu = 0 vif = [ 'mac=aa:00:00:00:00:0d,bridge=xen-br2' ] disk = [ 'phy:/dev/XENU/boss_,hda1,w', 'phy:/dev/XENU/bossswap,hda2,w', 'phy:/dev/XENU/boss_tmp,hda3,w', 'phy:/dev/XENU/boss_usr,hda4,w', 'phy:/dev/XENU/boss_var,hda5,w' ] if vminstall > 0: vif = [ 'mac=aa:00:00:aa:aa:aa,bridge=xen-br1' ] # Set if you want dhcp to allocate the IP address. dhcp = "dhcp" # Set netmask. #netmask= # Set default gateway. #gateway= # Set the hostname. hostname = "boss" # Set root device. root = "/dev/nfs" # provided by dhcp # The nfs server. #nfs_server = '' # Root directory on the nfs server. #nfs_root = '/usr/lib/fai/nfsroot' extra = "FAI_ACTION=install FAI_FLAGS=verbose,sshd,createvt,syslogd" else: root = "/dev/hda1 ro"
Well, that's it.
Further hints:
example configspace for xen domU's
- I use this configspace to install Xen DomU's: [Image:Fai-configspace.tar.gz] (it's a mix of simple examples, fai-distributions from people/lazyboy in Subversion, some additions for xen and some personal stuff...
combining FAI with xen-tools
- Here I wrote some things to use xen-tools and FAI together: Xen-tools and FAI softupdates
adjustments needed to the fai nfsroot
I use a script called tunenfsroot to make some adjustments for installing xen DomU's via network:
#!/bin/sh prefix=/usr/lib/fai/nfsroot touch /usr/lib/fai/nfsroot/.nocolorlogo # most of them stolen from xen-tools scripts... # von 30-fix-inittab sed -i -e 's/tty[0-9]$/console/g' -e 's/^\([2-6].*:respawn*\)/#\1/' -e 's/^T/#\t/' ${prefix}/etc/inittab # von 10-disable-tls mv ${prefix}/lib/tls ${prefix}/lib/tls.disabled mkdir ${prefix}/lib/tls # von 15-disable-hwclock chmod -x ${prefix}/etc/init.d/hwclock.sh chmod -x ${prefix}/etc/init.d/hwclockfirst.sh # von 55-create-dev cd ${prefix}/dev ./MAKEDEV generic ./MAKEDEV sd cp -a /lib/modules/* /usr/lib/fai/nfsroot/lib/modules/
initrd for netboot
For netinstalls, when using the default debian kernel, you also need a netboot-capable initrd. To get this, set "MODULES=netboot" in /etc/initramfs-tools/initramfs.conf and create a new initrrd. Use this only for installing the domU, otherwise use the normal initrd.