Migration OpenVZ to Xen (Debian)

I recently migrated my servers from Debian squeeze with OpenVZ to Debian 7 with Xen. The reason is that debian wheezy doesn’t contain any packages of OpenVZ in the official repositories. So I decided to migrate to Xen.

The steps to do that are:

1. Save container in image files
2. Install operating system (Debian)
3. Install virtualization (Xen)
4. Copy image files into newly created virtual machines
5. Prepare vms

Here are the detailed steps:

1 Create image files #

You have to create a image file for each container you have. The following code creates a 1GB image file: dd if=/dev/zero of=~/tmp/image.img bs=1M count=1024 Change the count number and the file will be smaller or greater. At least the image file should be as large as your container. To get the size of your container you can do:

du -sh /vz/root/$VEID/

Next you have to format your image file:

/sbin/mkfs.ext3 /tmp/image.img

and mount it in your file system:

mount -t ext3 -o loop /tmp/image.img /media/Imagemount

This will copy all files from container to your image file (-H is for hardlinks)

rsync -aAXHv --delete /vz/root/$VEID/* /media/Imagemount

2 Install operating system (Debian) #

2.1 Format disk #

If you are not able to install your debian normally, cause you have no physically access to the server, the next steps will prepare the installation with a rescue system: First you have to boot into rescue system.

Next you will erase your whole disk and create new partitions:

fdisk /dev/sda

We want to create for partitions:

1. Boot partition (300 MB)
2. Data partition (20 GB)
3. Swap space (double size of your ram)
4. LVM space for your virtual machines

Hint: To change the type of a partition to swap you have to enter „t“ and set the partition id to „82“ (partition id „8e“ for LVM). Save your changes with „w“.

2.2 Install raid #

This chapter is only neccessary if you want to install a RAID 1 (mirror).

Clone partition table to /dev/sdb

sfdisk -d /dev/sda | sfdisk --force /dev/sdb

Create raids

apt-get install mdadm

Create a raid for each partition:

mdadm -v --create /dev/md0 --level=mirror --raid-devices=2 /dev/sda1 /dev/sdb1
mdadm -v --create /dev/md1 --level=mirror --raid-devices=2 /dev/sda2 /dev/sdb2
mdadm -v --create /dev/md2 --level=mirror --raid-devices=2 /dev/sda3 /dev/sdb3
mdadm -v --create /dev/md3 --level=mirror --raid-devices=2 /dev/sda4 /dev/sdb4

Wait until synchronisation finished

watch cat /proc/mdstat

2.3 Format partitions #

Create swap partition

mkswap /dev/md2

Format boot partion

mkfs.ext3 /dev/md0

Format data partition

mkfs.ext4 /dev/md1

Create lvm volume

apt-get install lvm2
pvcreate /dev/md3
vgcreate vg0 /dev/md3

Mount data partition and create main folders

mount /dev/md1/ /mnt/
cd /mnt
mkdir etc
mkdir boot
mkdir var
mkdir usr
mkdir tmp
mkdir home

Mount boot partition into filesystem

mount /dev/md0 boot/

Edit fstab file to mount partitions on boot:

vi /mnt/etc/fstab

Insert the following lines:

proc /proc proc defaults 0 0
/dev/md0 /boot ext3 defaults 0 2
/dev/md1 / ext3 defaults 0 1
/dev/md2 none swap defaults,pri=1 0 0

2.4 Installation of debian #

Install debootstrap

apt-get install debootstrap

Download all sources from ftp.de.debian.org for debian wheezy and install it to /mnt/

debootstrap --arch amd64 wheezy /mnt/ http://ftp.de.debian.org/debian

Prepare to chroot into new debian

mount -t proc none /mnt/proc
mount -o bind /dev /mnt/dev
mount -o bind /sys /mnt/sys

chroot into system

chroot /mnt

Restore network settings.

vi /etc/network/interfaces

Set host name

vi /etc/hostname

Update system

apt-get update
apt-get install mdadm openssh-server lvm2 locales grub2 console-data

Set locales

dpkg-reconfigure locales

Installation of kernel

apt-get install linux-image-amd64

Installation of grub grub-install --no-floppy /dev/md0

Change password with passwd passwd

Reboot the system

exit

reboot

3 Install virtualization (Xen) #

3.1 Prepare OS for xen #

apt-get install bridge-utils

Create bridge interface

vi /etc/network/interfaces

You have to edit the lines with your internet connection interface

auto eth0
iface eth0 inet static
address 80.141.234.21
netmask 255.255.255.252
gateway 80.141.234.20

To something like that:

auto eth0
iface eth0 inet manual
auto xenbr0

iface xenbr0 inet static
bridge_ports eth0
address 80.141.234.21
netmask 255.255.255.252
gateway 80.141.234.20

3.2 Installation of xen #

apt-get install xen-linux-system

Change boot order

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

Reboot machine to run debian with debian-xen kernel

reboot

Install xen tools

apt-get install xen-tools

4. Copy image files into newly created virtual machines #

You have to create your vms. The command for this is

xen-create-image

After your vm has been created you have to mount the disk to copy your files in it

mount /dev/vg0/test-disk /mnt/test-disk

Next you can copy the files from your image file to your virtual disk

rsync -aAXHv /path/to/your/mounted/image/file/* /mnt/test-disk/

Now you have to make a few changes: Edit fstab to mount your disk.

vi /etc/fstab

The following lines should be fine for standard configuration:

proc /proc proc defaults 0 0
none /dev/pts devpts mode=0620 0 0
/dev/xvda1 none swap sw 0 0
/dev/xvda2 / ext4 noatime,nodiratime,errors=remount-ro 0 1

Edit inittab to load a console after boot vi /etc/inittab Add this line to the end: 1:2345:respawn:/sbin/getty 38400 hvc0

Now you can unmount (umount) your disk.

Edit the xen configuration file of your vm to add the bridge as your network interface. vi /etc/xen/test.cfg Change the line vif = [ 'mac=xx:xx...xx'] to something like that vif = [ 'mac=xx:xx...xx,bridge=xenbr0']

That’s it 🙂

Try to boot your vm with: xm create -c /etc/xen/test.cfg

Now you’re ready to have fun with Xen 🙂

If you want to add a internal network (for example for all your virtual machines) you have to add a new bridge:

vi /etc/network/interfaces

Add these lines:

auto eth0.100
iface eth0.100 inet manual

auto xenbr1
iface xenbr1 inet static
bridge_ports eth0.100
address 10.10.0.1
netmask 255.255.255.0

Edit your vm cfg

vi /etc/xen/test.cfg

Add a new interface

vif = [ 'mac=xx:xx...xx,bridge=xenbr0', 'mac=xx:xx...xx,bridge=xenbr1']

Reboot your vm and add the new interface in your /etc/network/interfaces

vi /etc/network/interfaces
auto eth1
iface eth1 inet static
address 10.10.0.2
netmask 255.255.255.0

Sources (English and German): http://blog.mellenthin.de/archives/2010/03/14/debian-lenny-auf-einem-rootserver-mit-raid-1-und-lvm/ http://wiki.xenproject.org/wiki/Xen_Beginners_Guide#Creating_a_Debian_PV_.28Paravirtualized.29_Guest https://wiki.debian.org/Xen