Izak Burger: Setting up Xen on a Hetzner EX4

There are many howtos out there. This one is mine.

The howtos that I consulted in setting this up were the following:

• Debian Wiki
• Ubuntu on Xen
• Xen auf Debian

The first thing I did was to upgrade the freshly provided Squeeze installation to Wheezy. This I did simply by editing /etc/apt/sources.list and replacing squeeze with wheezy, and commenting out the lines for backports. Then:

apt-get update
apt-get dist-upgrade

Now install the packages needed to run Xen:

apt-get install xen-linux-system xen-tools

Now prioritise the Xen kernels over the normal ones:

dpkg-divert --divert /etc/grub.d/08_linux_xen --rename /etc/grub.d/20_linux_xen
update-grub

For this specific setup, we ordered an extra /28 network for the Xen hosts. The first of these ip addresses were assigned to dom0 (the host itself) by changing /etc/network/interfaces. For this example, I use 172.16.150.224/28, but you should of course replace that with the real thing:

auto  eth0
iface eth0 inet static
  address   172.16.1.125
  broadcast 172.16.1.127
  netmask   255.255.255.224
  gateway   172.16.1.97
  up ip addr add 172.16.150.225/28 dev eth0

At this point you can reboot the machine, and it should come up in the xen kernel, which you can verify by running:

xm list

Next we need to edit a few network settings, by editing /etc/sysctl.conf:

net.ipv4.ip_forward=1
net.ipv4.conf.all.rp_filter=1
net.ipv4.conf.default.proxy_arp=1
net.ipv4.icmp_echo_ignore_broadcasts=1
net.ipv6.conf.all.forwarding = 1

Then reload network settings:

sysctl -p

Now edit /etc/xen/xend-config.sxp and configure as follows (comment out other settings):

(network-script network-route)
(vif-script     vif-route)
(dom0-min-mem 1024)
(enable-dom0-ballooning no)
(total_available_memory 0)
(dom0-cpus 0)
(vncpasswd '')

Then restart xen:

/etc/init.d/xen restart

Next you need to configure LVM. On this particular host, the bulk of the space was assigned to /home, which was unused as no user accounts had been created yet. Setting up LVM was therefore an easy task. First you edit /etc/fstab and remove /home from it. Assuming that /dev/md3 was mounted on /home, you then:

umount /home
pvcreate /dev/md3
vgcreate vg0 /dev/md3

Now configure xen-tools by editing /etc/xen-tools/xen-tools.conf. For this setup, we default to ubuntu 12.04:

lvm = vg0
install-method = debootstrap
size   = 120Gb      # Disk image size.
memory = 768Mb    # Memory size
swap   = 1536Mb    # Swap size
fs     = ext3     # use the EXT3 filesystem for the disk image.
dist   = precise
image  = sparse   # Specify sparse vs. full disk images.
gateway    = 172.16.150.225
netmask    = 255.255.255.240
broadcast  = 172.16.150.239
passwd = 1
kernel = /boot/vmlinuz-`uname -r`
initrd = /boot/initrd.img-`uname -r`
arch = amd64
mirror = http://archive.ubuntu.com/ubuntu/

Configure your firewall. I prefer using firehol for this sort of thing. First install firehol:

apt-get install firehol

Then edit /etc/firehol/firehol.conf:

version 5

FIREHOL_LOG_MODE="ULOG"

interface eth0 internet
    protection strong 500/sec
    server "icmp ssh http https" accept
    client all accept

# Allow traffic from eth0 to reach the XEN hosts
router xenr inface eth0 outface vif+
    server "icmp ssh http https" accept
    client all accept

Test your firewall:

firehol try

Then edit /etc/default/firehol and set:

START_FIREHOL=YES

Finally, build your first virtual host:

xen-create-image --hostname=guest1.example.com --ip=172.16.150.226

This will take quite a while, depending on the speed of your mirror. Start it:

xm create /etc/xen/guest1.example.com.cfg

You can view console with:

xm console guest1.example.com

And you can exit from the console using ctrl+]. You should also be able to ssh to the host.