HA cluster with DRBD and Heartbeat
This article shows how to setup a OpenVZ high availability (HA) cluster using the data replication software DRBD and the cluster manager Heartbeat. In this example the two machines builing the cluster run on CentOS 4.3. The article also shows how to do kernel updates in the cluster, including necessary steps like recompiling of new DRBD userspace tools. For this purpose, kernel 2.6.8-022stab078.10 (containing DRBD module 0.7.17) is used as initial kernel version, and kernel 2.6.8-022stab078.14 (containing DRBD module 0.7.20) as updated kernel version.
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
Contents
Prerequisites
The OpenVZ kernel already includes the DRBD module. The DRBD userspace tools and the cluster manager Heartbeat must be provided seperately. As the API version of the DRBD userspace tools must exactly match the API version of the module, compile them yourself. Also compile Heartbeat yourself, as at the time of this writing the CentOS extras repository only contained an old CVS version of Heartbeat.
On a hardware node for production use there should not be any applications that are not really needed for running OpenVZ (any things which are not needed by OpenVZ should run in a VE for security reasons). As a result, compile DRBD and Heartbeat on another machine running CentOS 4.3 (in this example I used a virtual machine on a VMware Server).
Compiling Heartbeat
Heartbeat version 1.2.* has successfully been used in a lot of two-node-clusters around the world. As the codebase used in version 1.2.* is in production use for many years now, the code is very stable. At the time of writing, Heartbeat version 1.2.4 is the current version of the 1.2.* branch.
Get tar.gz of the current version of the 1.2.* branch from http://linux-ha.org/download/index.html, at the time of this writing this is http://linux-ha.org/download/heartbeat-1.2.4.tar.gz. Use rpmbuild to build the package:
rpmbuild -ta heartbeat-1.2.4.tar.gz
After that, you find four rpm packes in /usr/src/redhat/RPMS/i386 (heartbeat-1.2.4-1.i386.rpm, heartbeat-ldirectord-1.2.4-1.i386.rpm, heartbeat-pils-1.2.4-1.i386.rpm, heartbeat-stonith-1.2.4-1.i386.rpm). In this example only heartbeat-1.2.4-1.i386.rpm is needed.
Compiling DRBD userspace tools
When compiling the DRBD userspace tools, you have to take care to take the version that matches the DRBD version that is included in the OpenVZ kernel you want to use. If you are unsure about the version, do the following steps while running the OpenVZ kernel that you want to use on a test machine (I used another virtual machine on a VMware server to try this):
[root@testmachine ~]# cat /proc/version Linux version 2.6.8-022stab078.10 (root@rhel4-32) (gcc version 3.4.5 20051201 (Red Hat 3.4.5-2)) #1 Wed Jun 21 12:01:20 MSD 2006 [root@testmachine ~]# modprobe drbd [root@testmachine ~]# cat /proc/drbd version: 0.7.17 (api:77/proto:74) SVN Revision: 2093 build by phil@mescal, 2006-03-06 15:04:12 0: cs:Unconfigured 1: cs:Unconfigured [root@testmachine ~]# rmmod drbd [root@testmachine ~]#
Here the version of the DRBD module is 0.7.17. So the userspace tools for 0.7.17 are neccessary.
Back on the buildmachine, do the following to create the rpm:
[root@buildmachine ~]# yum install kernel-devel gcc bison flex Setting up Install Process Setting up repositories Reading repository metadata in from local files Parsing package install arguments Nothing to do [root@buildmachine ~]# tar xfz drbd-0.7.17.tar.gz [root@buildmachine ~]# cd drbd-0.7.17 [root@buildmachine drbd-0.7.17]# make rpm KDIR=/usr/src/kernels/2.6.9-34.0.2.EL-i686/ [...] You have now: -rw-r--r-- 1 root root 288728 Jul 30 10:40 dist/RPMS/i386/drbd-0.7.17-1.i386.rpm -rw-r--r-- 1 root root 518369 Jul 30 10:40 dist/RPMS/i386/drbd-km-2.6.9_34.0.2.EL-0.7.17-1.i386.rpm [root@buildmachine drbd-0.7.17]#
Note that in this way the kernel-devel from CentOS is used, but this does not matter as the created drbd-km rpm will not be used (the DRBD kernel module is already included in OpenVZ kernel).
Installing the two nodes
Install the two machines in the same way as you would install them for a normal OpenVZ installation, but do not create a filesystem for the /vz. This filesystem will be installed later on on top of DRBD.
| Parameter | node1 | node2 |
|---|---|---|
| hostname | ovz-node1 | ovz-node2 |
| / filesystem | hda1, 10 GB | hda1, 10 GB |
| swap space | hda2, 2048 MB | hda2, 2048 MB |
| public LAN | eth0, 192.168.1.201 | eth0, 192.168.1.202 |
| private LAN | eth1, 192.168.255.1 (Gbit Ethernet) | eth1, 192.168.255.2 (Gbit Ethernet) |
| other install options | no firewall, no SELinux | no firewall, no SELinux |
| package groups | deactivated everything, only kept vim-enhanced | deactivated everything, only kept vim-enhanced |
Installing OpenVZ
Get the OpenVZ kernel and utilities and install them on both nodes, as described in quick installation. Update grub configuration to use the OpenVZ kernel by default and reboot both machines.
Setting up DRBD
On each of the two nodes create a partition that acts as underlying DRBD device. The partitions should have exectly 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 ~]# rpm -ihv drbd-0.7.17-1.i386.rpm Preparing... ########################################### [100%] 1:drbd ########################################### [100%] [root@ovz-node1 ~]#
Then create the drbd.conf configuration file and copy it to /etc/drbd.conf on both nodes. Below is the example configuration file that is used in this article:
resource r0 {
protocol C;
incon-degr-cmd "echo '!DRBD! pri on incon-degr' | wall ; sleep 60 ; halt -f";
startup {
degr-wfc-timeout 120;
}
net {
on-disconnect reconnect;
}
disk {
on-io-error detach;
}
syncer {
rate 30M;
group 1;
al-extents 257;
}
on ovz-node1 {
device /dev/drbd0;
disk /dev/hda3;
address 192.168.255.1:7788;
meta-disk internal;
}
on ovz-node2 {
device /dev/drbd0;
disk /dev/hda3;
address 192.168.255.2:7788;
meta-disk internal;
}
}
Start DRBD on both nodes:
[root@ovz-node1 ~]# /etc/init.d/drbd start Starting DRBD resources: [ d0 s0 n0 ]. [root@ovz-node1 ~]#
Then check the status of /proc/drbd:
[root@ovz-node1 ~]# cat /proc/drbd
version: 0.7.17 (api:77/proto:74)
SVN Revision: 2093 build by phil@mescal, 2006-03-06 15:04:12
0: cs:Connected st:Secondary/Secondary ld:Inconsistent
ns:0 nr:0 dw:0 dr:0 al:0 bm:0 lo:0 pe:0 ua:0 ap:0
[root@ovz-node1 ~]#
Both nodes are now Secondary and Inconsistent. The latter is because the underlying storage is not yet in-sync, and DRBD has no way to know whether you want the initial sync from ovz-node1 to ovz-node2, or ovz-node2 to ovz-node1. As there is no data below it yet, it does not matter.
To start the sync from ovz-node1 to ovz-node2, do the following on ovz-node1:
[root@ovz-node1 ~]# drbdadm -- --do-what-I-say primary all
[root@ovz-node1 ~]# cat /proc/drbd
version: 0.7.17 (api:77/proto:74)
SVN Revision: 2093 build by phil@mescal, 2006-03-06 15:04:12
0: cs:SyncSource st:Primary/Secondary ld:Consistent
ns:627252 nr:0 dw:0 dr:629812 al:0 bm:38 lo:640 pe:0 ua:640 ap:0
[=>..................] sync'ed: 6.6% (8805/9418)M
finish: 0:04:51 speed: 30,888 (27,268) K/sec
[root@ovz-node1 ~]#
As you see, DRBD syncs with about 30 MB per second, as we told it so in /etc/drbd.conf. On the SyncSource (ovz-node1 in this case) the DRBD device is already useable (although it is syncing in the background).
So you can immediately create the filesystem:
[root@ovz-node1 ~]# mkfs.ext3 /dev/drbd0 [...] [root@ovz-node1 ~]#
Copy necessary OpenVZ files to DRBD device
Currently, ovz-node1 is still Primary of /dev/drbd0. You can now mount it and copy the necessary files to it (only on ovz-node1!):
[root@ovz-node1 ~]# mount /dev/drbd0 /mnt [root@ovz-node1 ~]# cp -a /vz/* /mnt/ [root@ovz-node1 ~]# mkdir -p /mnt/cluster/etc/sysconfig [root@ovz-node1 ~]# mkdir -p /mnt/cluster/var [root@ovz-node1 ~]# cp -a /etc/sysconfig/vz /mnt/cluster/etc/sysconfig [root@ovz-node1 ~]# cp -a /etc/sysconfig/vz-scripts /mnt/cluster/etc/sysconfig [root@ovz-node1 ~]# cp -a /var/vzquota /mnt/cluster/var [root@ovz-node1 ~]# umount /dev/drbd0 [root@ovz-node1 ~]#
Afterwards move the original files and replace them with symbolic links (do this on both nodes):
[root@ovz-node1 ~]# mv /etc/sysconfig/vz /etc/sysconfig/vz.orig [root@ovz-node1 ~]# mv /etc/sysconfig/vz-scripts /etc/sysconfig/vz-scripts.orig [root@ovz-node1 ~]# mv /var/vzquota /var/vzquota.orig [root@ovz-node1 ~]# ln -s /vz/cluster/etc/sysconfig/vz /etc/sysconfig/vz [root@ovz-node1 ~]# ln -s /vz/cluster/etc/sysconfig/vz-scripts /etc/sysconfig/vz-scripts [root@ovz-node1 ~]# ln -s /vz/cluster/var/vzquota /var/vzquota [root@ovz-node1 ~]#
Setting up Heartbeat
(I'll update this part soon)
How to do OpenVZ kernel updates when it contains a new DRBD version
(I'll update this part soon)
How to do updates of vzctl, vzctl-lib, and vzquota
(I'll update this part soon)