Create Xen DomU Xen-Tools template

Damian 3 Comments

First there are a few things to consider and configure before creating new virtual machines (DomU).

Loopback vs LVM

Transfering a file is easier than moving lvm volumes to servers.
As the DomU will run services in production, lvm is the better choice.
Other possibilities for more portability: Docker, XenServer Cluster, OpenStack

XL config

Modify /etc/xen/xl.conf to equip the xl toolstack with neccessary environment.

autoballoon="off"
lockfile="/var/lock/xl"
vif.default.gatewaydev="eth0"
vif.default.bridge="xenbr0"

Partition template

Create template file: /etc/xen-tools/partitions.d/server

As rights, permissions and performance can be set per disk partition a proper setup is recommended (but not neccessary). This template is used only with parameter –partitions=server using xen-create-image.

[root]
size=20G
type=ext4
mountpoint=/
options=errors=remount-ro

[opt]
size=5G
type=xfs
mountpoint=/opt
options=nodev

[tmp]
size=2.5G
type=xfs
mountpoint=/tmp
options=nodev,nosuid

[usr]
size=10G
type=xfs
mountpoint=/usr
options=nodev

[var]
size=10G
type=xfs
mountpoint=/var
options=nodev,nosuid

[var-tmp]
size=2.5G
type=xfs
mountpoint=/var/tmp
options=nodev,nosuid

[var-www]
size=100G
type=ext4
mountpoint=/var/www
options=relatime,nodev,nosuid

[var-srv]
size=100G
type=ext4
mountpoint=/var/srv
options=relatime,nodev

Deposit public ready to spread to new virtual machines

To have keybased login working in the new vms the public key is stored in the skeleton directory of xen-tools.

mkdir -p /etc/xen-tools/skel/root/.ssh
chmod -R 700 /etc/xen-tools/skel/root
# If you don't have ssh key - run ssh-keygen to create
ssh-keygen
cp /root/.ssh/id_rsa.pub /etc/xen-tools/skel/root/.ssh/authorized_keys

Create xen vm role

To customize a xen install, we could use custom hooks or roles.
The role file could be extended to launch and preconfigure puppet client. To adopt look at: /etc/xen-tools/roles.d/puppet
Create a role: /etc/xen-tools/roles.d/server

Purpose of this role file

  • Create Hetzner network configuration based on ipv4 list
  • Create Hetzner network configuration based on ipv6 list
  • Install few tools (htop, screen…)
  • Create message of the day (Use your own ASCII logo)
  • Create locale files and set de_DE.UTF-8 as default
# create and make executable
touch /etc/xen-tools/roles.d/server
chmod +x /etc/xen-tools/roles.d/server
#!/bin/bash

prefix=$1

#
#  Source our common functions
#
if [ -e /usr/share/xen-tools/common.sh ]; then
    . /usr/share/xen-tools/common.sh
else
    echo "Installation problem"
fi

#
# network config
#

if [ -f ${prefix}/etc/network/interfaces ]; then

  cat << EOF > ${prefix}/etc/network/interfaces
# loopback
auto lo
iface lo inet loopback
EOF

  # ipv4 of host system
  host_ipv4=$(ifconfig xenbr0 2>/dev/null|awk '/inet addr:/ {print $2}'|sed 's/addr://')

  # if /etc/xen-tools/ipv4-list.conf exist use these values, otherwise use parameter
  if [ -f "/etc/xen-tools/ipv4-list.conf" ]; then
    ipv4row=$(grep "${hostname}\$" /etc/xen-tools/ipv4-list.conf)
    if [ ! -z "${ipv4row}" ] ; then
      # extract ip values of ipv4-list.conf
      ipv4regex='^([0-9.]+);([0-9.]+);([0-9.]+);.*$'
      [[ "$ipv4row" =~ $ipv4regex ]] && { add_ipv4=${BASH_REMATCH[1]} ; add_netmaskv4=${BASH_REMATCH[2]} ; add_gatewayv4=${BASH_REMATCH[3]} ; }
      # append to interfaces-file
      cat << EOF >> ${prefix}/etc/network/interfaces

# internet
auto eth0
iface eth0 inet static
 address ${add_ipv4}
 gateway ${add_gatewayv4}
 netmask ${add_netmaskv4}
 pointopoint ${add_gatewayv4}
EOF

    else
      # append to interface-file if ipv4-list.conf not matching
      cat << EOF >> ${prefix}/etc/network/interfaces

# internet
auto eth0
iface eth0 inet static
 address ${ip1}
 gateway ${gateway}
 netmask ${netmask}
 #pointopoint ${host_ipv4}
EOF

    fi
  fi


  # if /etc/xen-tools/ipv6-list.conf exist use these values
  if [ -f "/etc/xen-tools/ipv6-list.conf" ]; then
    ipv6row=$(grep "${hostname}\$" /etc/xen-tools/ipv6-list.conf)
    if [ ! -z "${ipv6row}" ] ; then
      # extract ip ipv6-list.conf
      ipv6regex='^([0-9A-Fa-f:]+);([0-9]+);.*$'
      [[ "$ipv6row" =~ $ipv6regex ]] && { add_ipv6=${BASH_REMATCH[1]} ; add_subnetv6=${BASH_REMATCH[2]} ; }

      # append to interfaces-file
      cat << EOF >> ${prefix}/etc/network/interfaces

iface eth0 inet6 static
 address ${add_ipv6}
 netmask 80
 up ip -6 route add default via fe80::1 dev eth0
EOF

    fi
  fi

fi

cat << EOF > ${prefix}/etc/motd

                   ___                      ____
                  / __| __ _ _ ___ ___ _ _ |_  /___ _ _  ___
                  \__ \/ _| '_/ -_) -_) ' \ / // _ \ ' \/ -_)
                  |___/\__|_| \___\___|_||_/___\___/_||_\___|

                  ${hostname} | ${ip1} | ${add_ipv6}

EOF

#
# Install additional Packages
#
installDebianPackage ${prefix} obnam fail2ban ntpdate ntp screen htop iftop iotop psmisc rsync

#
# Locale Settings
#
echo "export LANGUAGE=de_DE.UTF-8" >>${prefix}/etc/profile
echo "export LANG=de_DE.UTF-8" >>${prefix}/etc/profile
echo "export LC_ALL=de_DE.UTF-8" >>${prefix}/etc/profile
chroot ${prefix} locale-gen de_DE.UTF-8

#
# Log our finish
#
logMessage Script $0 finished

Configuration

For ip address assignment there are configuration files to be filled.
Since Xen is missing network management, it has to be configured manually (using the role script above and config files underneath).
My solution is only a quick hack working with Hetzner network environment. Adopt it and modify it to your needs!

IP list configuration files

Create files and setup you additional ips.

vi /etc/xen-tools/ipv6-list.conf

# ipv6 ; subnet ; vm hostname
W:X:Y:Z:1::1;80;srv-xy-1
W:X:Y:Z:2::1;80;srv-xy-2

vi /etc/xen-tools/ipv4-list.conf

# ip ; netmask ; gateway ; vm hostname (optional)
A.A.A.A;255.255.255.224;GW.GW.GW.GW;srv-xy-1
B.B.B.B;255.255.255.248;GW2.GW2.GW2.GW2;srv-xy-2

Using these two configuration files, the role file “server” and xen-create-image with hostname=srv-xy-1, a network configuration within the vm will be created with eth0 ipv4 A.A.A.A, gateway GW.GW.GW.GW and netmask 255.255.255.224 (this may vary based on what Hetzer is going to assign). Also a eth0 ipv6 will be created with W:X:Y:Z:1::1, netmask 80.

If there is no hostname matching in ipv6 config files, the parameter of xen-create-image will be used. Example:

xen-create-image [..] --hostname=srv-name-not-in-list --ip=A.A.A.A --gateway=Gw.GW.GW.GW --netmask=255.255.255.224 [..]

Configure screen

Use this screen configuration in .screenrc config file for fancy and smart screen layout.

This config provides functions like resize regions, step through windows using F3/F4 and nicer layout.
Deposit the file here: /etc/xen-tools/skel/root/.screenrc

# ===============================================================
# VARIABLES - Boolean values (on/off)
# ===============================================================

# mousetrack            on              # mouse tracking support
  autodetach            on              # default: on
  crlf                  off             # default: off
  defbce                on
  deflogin              off             # default: on
# defsilence            off             # default: off
  hardcopy_append       on              # default: off
# nethack               on              # default: off
  startup_message       off             # default: on
  vbell                 off             # default: ???

# 256 colors
attrcolor b ".I"
termcapinfo xterm 'Co#256:AB=\E[48;5;%dm:AF=\E[38;5;%dm'

# mouse support in screen
term rxvt

# this makes screen work within rxvt on cygwin:
termcapinfo rxvt-cygwin-native ti@:te@
# make the cursor show up in red:
termcapinfo linux “ve=\E[?25h\E[?17;0;64c”

# the following two lines give a two-line status, with the current window highlighted
hardstatus alwayslastline
hardstatus string '%{gk}[ %{G}%H %{g}][%= %{wk}%?%-Lw%?%{=b kR}(%{W}%n*%f %t%?(%u)%?%{=b kR})%{= kw}%?%+Lw%?%?%= %{g}][%{Y}%l%{g}]%{=b C}[ %Y-%m-%d %c ]%{W}'

# huge scrollback buffer
defscrollback 5000

# ===============================================================
# AUTOSTART
# ===============================================================

# default windows
screen -t bash  1 bash
select 0
bind c screen 1 # window numbering starts at 1 not 0
bind 0 select 10

# get rid of silly xoff stuff
bind s split

# ===============================================================
# LAYOUT
# ===============================================================

layout autosave on
layout new one
select 1
layout new two
select 1
split
resize -v +8
focus down
select 4
focus up
layout new three
select 1
split
resize -v +7
focus down
select 3
split -v
resize -h +10
focus right
select 4
focus up

layout attach one
layout select one

# ===============================================================
# KEY BINDINGS
# ===============================================================

# navigating regions with Ctrl-arrows
bindkey "^[[1;5D" focus left
bindkey "^[[1;5C" focus right
bindkey "^[[1;5A" focus up
bindkey "^[[1;5B" focus down

# switch windows with F3 (prev) and F4 (next)
bindkey "^[OR" prev
bindkey "^[OS" next

# switch layouts with Ctrl+F3 (prev layout) and Ctrl+F4 (next)
bindkey "^[O1;5R" layout prev
bindkey "^[O1;5S" layout next

# F2 puts Screen into resize mode. Resize regions using hjkl keys.
bindkey "^[OQ" eval "command -c rsz" # enter resize mode

# use hjkl keys to resize regions
bind -c rsz h eval "resize -h -5" "command -c rsz"
bind -c rsz j eval "resize -v -5" "command -c rsz"
bind -c rsz k eval "resize -v +5" "command -c rsz"
bind -c rsz l eval "resize -h +5" "command -c rsz"

# quickly switch between regions using tab and arrows
bind -c rsz \t    eval "focus"       "command -c rsz" # Tab
bind -c rsz -k kl eval "focus left"  "command -c rsz" # Left
bind -c rsz -k kr eval "focus right" "command -c rsz" # Right
bind -c rsz -k ku eval "focus up"    "command -c rsz" # Up
bind -c rsz -k kd eval "focus down"  "command -c rsz" # Down

Start Xen VM for demo

Finished with customizing.
Although a firewall is needed for production use, the functional part is still working.
Give it a try by initialising a demo vm.

xen-create-image --hostname=srv-xy-1 --role=server&nbsp;--partitions=server --dist=jessie --vcpus=4 --memory=4G --maxmem=6G --size=50G --noswap --ip=A.A.A.A --mac=A:B:C:D:E:F

# connect to console after finishing install
xl console srv-xy-1

Login to your demo. Disconnect using key combo: CTRL+[

3 thoughts on “Create Xen DomU Xen-Tools template”

  1. Hi Damien,

    Great guide how we interested in knowing how to configure public interfaces for DomU.

    I have three IPs in total on a Hetzner server and would like to create two guests each with own ip. All Xen docs are not really clear

    Reply

  2. Damian, great tutorial! Thanks a lot!

    fstab option sync is causing performance gaps:

    options=sync...

    Removing it from config improved disk speed.

    Reply

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