Migration Xen

Introduction

Here is a howto to migrate domU from hosts to hosts under Ubuntu. There is multiple solutions.

Migration by rsync is recommended.

Migration by dd

On each host

• Create a logical volume to host the image

lvcreate -L5G -n migrate vg_hostname

• Format them in ext3

mkfs.ext3 /dev/vg_hostname/migrate

• Mount them in the filesystem

mkdir /mnt/migrate
mount /dev/vg_hostname/migrate /mnt/migrate/ 

On source host

• Create a snapshot of the running domU root disk

source # lvcreate -L4G -s -n service-disk-snap /dev/vg_hostname/service-disk

• Stop the service

source # xm shutdown service

• Do the byte to byte copy

source # dd if=/dev/vg_hostname/service-disk-snap conv=noerror,sync bs=64k | dd of=/mnt/migrate/service.dd bs=64k

• Transfer the file by scp

source # scp /mnt/migrate/service.dd destination:/mnt/migrate/

• Remove immediatly the snapshot

source # lvremove /dev/vg_hostname/service-disk-snap 

On destination host

• Create the new domU root disk

destination # lvcreate -L4G -n service-disk vg_hostname

• Create the new dom swap disk

destination # lvcreate -L256M -n service-swap vg_hostname

• Initiate the swap disk

destination # mkswap /dev/vg_hostname/service-swap

• Do the byte to byte copy (filesystem is contained in the dd image)

destination # dd if=/mnt/migrate/service.dd conv=noerror,sync bs=64k | dd of=/dev/vg_hostname/service-disk bs=64k

• Adapt and start the domU

destination # xm create /etc/xen/service.cfg 

Migration by rsync

On destination host

• Create the service root volume on destination and format it.

destination # lvcreate -L4G -n service-disk vg_hostname
destination # mkfs.ext3 /dev/vg_hostname/service-disk

• Create the service swap volume on destination and format it.

destination # lvcreate -L256M -n service-swap vg_hostname
destination # mkswap /dev/vg_hostname/service-swap

• Mount service root volume destination under, by e.g., /mnt/migrate

destination # mount /dev/vg_hostname/service-disk /mnt/migrate/

On source host

• Stop the domU on source.

source # xm shutdown service 

• Mount domU volume under, by e.g., /mnt/migrate

source # mount /dev/vg_hostname/service-disk /mnt/migrate/

• Do the copy :

source # rsync --numeric-ids --verbose --archive --bwlimit=100000 --rsh ssh /mnt/migrate/ destination:/mnt/migrate 

On destination host

• Adapt the .cfg of the service with new disk volume path and start the domain.

destination # xm create /etc/xen/service.cfg

Useful commands (exemple of maintenance)

On dest

lvcreate -L2G -n dhcp-disk rootvg
lvcreate -L512M -n dhcp-swap rootvg
lvcreate -L2G -n dns-disk rootvg
lvcreate -L512M -n dns-swap rootvg
lvcreate -L4G -n ldap-master-disk rootvg
lvcreate -L512M -n ldap-master-swap rootvg
lvcreate -L4G -n mail-disk rootvg
lvcreate -L512M -n mail-swap rootvg
lvcreate -L4G -n puppet-disk rootvg
lvcreate -L1G -n puppet-swap rootvg
lvcreate -L4G -n puppet-master-disk rootvg
lvcreate -L1G -n puppet-master-swap rootvg
for i in $(cat ~g5kadmin/vm_to_migrate); do echo "--> mkfs for vm $i..."; mkfs.ext3 /dev/rootvg/$i-disk; done
for i in $(cat ~g5kadmin/vm_to_migrate); do echo "--> mkswap for vm $i..."; mkswap /dev/rootvg/$i-swap; done
for i in $(cat ~g5kadmin/vm_to_migrate); do echo "--> Update kernel and ramdisk xen parameters for vm $i..."; sed -i "s/^\(kernel.*= \).*$/\1\'\/boot\/vmlinuz-`uname -r`\'/g" /etc/xen/$i.cfg; done
for i in $(cat ~g5kadmin/vm_to_migrate); do echo "--> Update kernel and ramdisk xen parameters for vm $i..."; sed -i "s/^\(ramdisk.*= \).*$/\1\'\/boot\/initrd.img-`uname -r`\'/g" /etc/xen/$i.cfg; done
for i in $(cat ~g5kadmin/vm_to_migrate); do echo "--> Update kernel bridges for vm $i..."; sed -i "s/bridge=eth1/bridge=xenbr0/g" /etc/xen/$i.cfg; done
for i in $(cat ~g5kadmin/vm_to_migrate); do echo "--> Update kernel bridges for vm $i..."; sed -i "s/bridge=eth0/bridge=xenbr1/g" /etc/xen/$i.cfg; done
for i in $(cat ~g5kadmin/vm_to_migrate); do echo "--> Update lvg name for vm $i..."; sed -i "s/paraquad-srv/rootvg/g" /etc/xen/$i.cfg; done
for i in $(cat ~g5kadmin/vm_to_migrate); do mkdir /tmp/$i; mount /dev/rootvg/$i-disk /tmp/$i; done

On source

for i in $(cat ~g5kadmin/vm_to_migrate); do echo "--> migrate xen $i.cfg file to parapluie-srv..."; scp /etc/xen/$i.cfg parapluie-srv:/etc/xen/; done
for i in $(cat ~g5kadmin/vm_to_migrate); do xm shutdown $i; done
for i in $(cat ~g5kadmin/vm_to_migrate); do mkdir /tmp/$i; mount /dev/paraquad-srv/$i-disk /tmp/$i; done
for i in $(cat ~g5kadmin/vm_to_migrate); do echo "--> migrate content of vms to parapluie-srv..."; rsync --numeric-ids --archive --rsh ssh /tmp/$i/ 131.254.203.41:/tmp/$i; done

other commands...

• on source :

for i in $(cat vm2migrate); do VM_NAME=$i; DISK_SIZE=$(lvdisplay --columns | grep "$VM_NAME-disk" | awk '{print $4;}'); SWAP_SIZE=$(lvdisplay --columns | grep "$VM_NAME-swap" | awk '{print $4;}'); echo "$VM_NAME;$DISK_SIZE;$SWAP_SIZE"; done > vm2migrate2
for i in $(cat vm2migrate); do VM_NAME=$(echo $i | cut -d";" -f1); scp /etc/xen/$VM_NAME.cfg adminfront:/etc/xen; done

• on target :

for i in $(cat vm2migrate); do VM_NAME=$(echo $i | cut -d";" -f1); DISK_SIZE=$(echo $i | cut -d";" -f2); SWAP_SIZE=$(echo $i | cut -d";" -f3); echo "--> create $VM_NAME-disk"; lvcreate -n $VM_NAME-disk -L$DISK_SIZE rootvg; echo "--> create $VM_NAME-swap"; lvcreate -n $VM_NAME-swap -L$SWAP_SIZE rootvg; done
for i in $(cat vm2migrate); do VM_NAME=$(echo $i | cut -d";" -f1); echo "--> $VM_NAME"; mkfs.ext3 /dev/rootvg/$VM_NAME-disk; mkswap /dev/rootvg/$VM_NAME-swap; done
for i in $(cat vm2migrate); do VM_NAME=$(echo $i | cut -d";" -f1); echo "--> $VM_NAME"; mkdir /tmp/vms/$VM_NAME-disk; mount /dev/rootvg/$VM_NAME-disk /tmp/vms/$VM_NAME-disk; done

... rsync...