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<b>Update:</b> this howto currently does not describe details on OpenVZ Kernel 2.6.18, which contains DRBD version 8.*. Meanwhile, some hints on using OpenVZ Kernel 2.6.18 with DRBD 8 can be found in [http://forum.openvz.org/index.php?t=msg&th=3213&start=0& this thread in the forum].
Additional information about clustering of virtual machines can be found in the following paper: [http://www.linuxtag.org/2006/fileadmin/linuxtag/dvd/12080-paper.pdf(PDF, 145K)]
Some other additional information can be found in the documentation of the Thomas-Krenn.AG cluster (The author of this howto is working in the cluster development there, that is the reason why he was able to write this howto :-). The full documentation with interesting illustrations is currently only [http://www.thomas-krenn.com/en/service-support/knowledge-center/cluster/documentation.html available in German]:
An excellent presentation and overview by Werner Fischer, Thomas-Krenn.AG is available here http://www.profoss.eu/index.php/main/content/download/355/3864/file/werner-fischer.pdf.
== Prerequisites ==
! other install options
| no firewall, no SELinux
| no firewall, no SELinux|-! package groups| deactivated everything, only kept vim-enhanced| deactivated everything, only kept SELinuxt vim-enhanced
|}
== Setting up DRBD ==
'''On each of the two nodes create a partition that acts as underlying DRBD device. ''' The partitions should have exactly the same size (I created a 10 GB partition hda3 using fdisk on each node for this example). Note that it might be necessary to reboot the machines to re-read the partition table.
Install the rpm of the DRBD userspace tools on both nodes:
[root@ovz-node1 ~]# mkdir -p /vz/cluster/etc/sysconfig
[root@ovz-node1 ~]# mkdir -p /vz/cluster/var
[root@ovz-node1 ~]# cp -a /etc/vz .orig /vz/cluster/etc/vz/[root@ovz-node1 ~]# cp -a /etc/sysconfig/vz-scripts .orig /vz/cluster/etc/sysconfig/vz-scripts[root@ovz-node1 ~]# cp -a /var/vzquota .orig /vz/cluster/var/vzquota
[root@ovz-node1 ~]# umount /dev/drbd0
[root@ovz-node1 ~]#
[root@ovz-node1 ~]# chkconfig vz off
[root@ovz-node1 ~]#
</pre>
== Live-Switchover with the help of checkpointing ==
With the help of [[Checkpointing_and_live_migration|checkpointing]] it is possible to do live switchovers.
<b>Important:</b> although this HOWTO currently describes the use of DRBD 0.7, it is necessary to use DRBD 8 to be able to use this live-switchover feature reliable. Some hints on using OpenVZ Kernel 2.6.18 with DRBD 8 can be found in [http://forum.openvz.org/index.php?t=msg&th=3213&start=0& this thread in the forum].
The following scripts are written by Thomas Kappelmueller. They should be placed at /root/live-switchover/ on both nodes. To activate the scripts execute the following commands on both nodes:
<pre>
[root@ovz-node1 ~]# ln -s /root/live-switchover/openvz /etc/init.d/
[root@ovz-node1 ~]# ln -s /root/live-switchover/live_switchover.sh /root/bin/
[root@ovz-node1 ~]#
</pre>
It is also necessary to replace <code>vz</code> by an adjusted initscript (<code>openvz</code> in this example). So /etc/ha.d/haresources has the following content on both nodes:
<pre>
ovz-node1 drbddisk::r0 Filesystem::/dev/drbd0::/vz::ext3 openvz MailTo::youremail@yourdomain.tld
</pre>
=== Script cluster_freeze.sh ===
<pre>
#!/bin/bash
#Script by Thomas Kappelmueller
#Version 1.0
LIVESWITCH_PATH='/vz/cluster/liveswitch'
if [ -f $LIVESWITCH_PATH ]
then
rm -f $LIVESWITCH_PATH
fi
RUNNING_VE=$(vzlist -1)
for I in $RUNNING_VE
do
BOOTLINE=$(cat /etc/sysconfig/vz-scripts/$I.conf | grep -i "^onboot")
if [ $I != 1 -a "$BOOTLINE" = "ONBOOT=\"yes\"" ]
then
vzctl chkpnt $I
if [ $? -eq 0 ]
then
vzctl set $I --onboot no --save
echo $I >> $LIVESWITCH_PATH
fi
fi
done
exit 0
</pre>
=== Script cluster_unfreeze.sh ===
<pre>
#!/bin/bash
#Script by Thomas Kappelmueller
#Version 1.0
LIVESWITCH_PATH='/vz/cluster/liveswitch'
if [ -f $LIVESWITCH_PATH ]
then
FROZEN_VE=$(cat $LIVESWITCH_PATH)
else
exit 1
fi
for I in $FROZEN_VE
do
vzctl restore $I
if [ $? != 0 ]
then
vzctl start $I
fi
vzctl set $I --onboot yes --save
done
rm -f $LIVESWITCH_PATH
exit 0
</pre>
=== Script live_switchover.sh ===
<pre>
#!/bin/bash
#Script by Thomas Kappelmueller
#Version 1.0
ps -eaf | grep 'vzctl enter' | grep -v 'grep' > /dev/null
if [ $? -eq 0 ]
then
echo 'vzctl enter is active. please finish before live switchover.'
exit 1
fi
ps -eaf | grep 'vzctl exec' | grep -v 'grep' > /dev/null
if [ $? -eq 0 ]
then
echo 'vzctl exec is active. please finish before live switchover.'
exit 1
fi
echo "Freezing VEs..."
/root/live-switchover/cluster_freeze.sh
echo "Starting Switchover..."
/usr/lib64/heartbeat/hb_standby
</pre>
=== Script openvz ===
<pre>
#!/bin/bash
#
# openvz Startup script for OpenVZ
#
start() {
/etc/init.d/vz start > /dev/null 2>&1
RETVAL=$?
/root/live-switchover/cluster_unfreeze.sh
return $RETVAL
}
stop() {
/etc/init.d/vz stop > /dev/null 2>&1
RETVAL=$?
return $RETVAL
}
status() {
/etc/init.d/vz status > /dev/null 2>&1
RETVAL=$?
return $RETVAL
}
# See how we were called.
case "$1" in
start)
start
;;
stop)
stop
;;
status)
status
;;
*)
echo $"Usage: openvz {start|stop|status}"
exit 1
esac
exit $RETVAL
</pre>
[[Category: HOWTO]]
