What this tutorial is: An in-depth walk-through of how to get Pacemaker to manage a KVM guest instance and integrate that guest into the cluster as a guest node.
What this tutorial is not: A realistic deployment scenario. The steps shown here are meant to get users familiar with the concept of guest nodes as quickly as possible.
Note
For this example, we will use a single physical host named example-host. A production cluster would likely have multiple physical hosts, in which case you would run the commands here on each one, unless noted otherwise.
On the physical host, allow cluster-related services through the local firewall:
# firewall-cmd --permanent --add-service=high-availability success # firewall-cmd --reload success
Note
If you are using iptables directly, or some other firewall solution besides firewalld, simply open the following ports, which can be used by various clustering components: TCP ports 2224, 3121, and 21064, and UDP port 5405.
If you run into any problems during testing, you might want to disable the firewall and SELinux entirely until you have everything working. This may create significant security issues and should not be performed on machines that will be exposed to the outside world, but may be appropriate during development and testing on a protected host.
To disable security measures:
[root@pcmk-1 ~]# setenforce 0 [root@pcmk-1 ~]# sed -i.bak "s/SELINUX=enforcing/SELINUX=permissive/g" /etc/selinux/config [root@pcmk-1 ~]# systemctl mask firewalld.service [root@pcmk-1 ~]# systemctl stop firewalld.service [root@pcmk-1 ~]# iptables --flush
# yum install -y pacemaker corosync pcs resource-agents
Corosync handles pacemaker's cluster membership and messaging. The corosync
config file is located in /etc/corosync/corosync.conf. That config file must
be initialized with information about the cluster nodes before pacemaker can
start.
To initialize the corosync config file, execute the following pcs command,
replacing the cluster name and hostname as desired:
# pcs cluster setup --force --local --name mycluster example-host
Note
If you have multiple physical hosts, you would execute the setup command on only one host, but list all of them at the end of the command.
Create a place to hold an authentication key for use with pacemaker_remote:
# mkdir -p --mode=0750 /etc/pacemaker # chgrp haclient /etc/pacemaker
Generate a key:
# dd if=/dev/urandom of=/etc/pacemaker/authkey bs=4096 count=1
Note
If you have multiple physical hosts, you would generate the key on only one host, and copy it to the same location on all hosts.
Start the cluster
# pcs cluster start
Verify corosync membership
# pcs status corosync
Membership information
----------------------
Nodeid Votes Name
1 1 example-host (local)
Verify pacemaker status. At first, the output will look like this:
# pcs status Cluster name: mycluster WARNING: no stonith devices and stonith-enabled is not false Stack: corosync Current DC: NONE Last updated: Fri Jan 12 15:18:32 2018 Last change: Fri Jan 12 12:42:21 2018 by root via cibadmin on example-host 1 node configured 0 resources configured Node example-host: UNCLEAN (offline) No active resources Daemon Status: corosync: active/disabled pacemaker: active/disabled pcsd: active/enabled
After a short amount of time, you should see your host as a single node in the cluster:
# pcs status Cluster name: mycluster WARNING: no stonith devices and stonith-enabled is not false Stack: corosync Current DC: example-host (version 1.1.16-12.el7_4.5-94ff4df) - partition WITHOUT quorum Last updated: Fri Jan 12 15:20:05 2018 Last change: Fri Jan 12 12:42:21 2018 by root via cibadmin on example-host 1 node configured 0 resources configured Online: [ example-host ] No active resources Daemon Status: corosync: active/disabled pacemaker: active/disabled pcsd: active/enabled
Now, enable the cluster to work without quorum or stonith. This is required for the sake of getting this tutorial to work with a single cluster node.
# pcs property set stonith-enabled=false # pcs property set no-quorum-policy=ignore
Warning
The use of stonith-enabled=false is completely inappropriate for a production
cluster. It tells the cluster to simply pretend that failed nodes are safely
powered off. Some vendors will refuse to support clusters that have STONITH
disabled. We disable STONITH here only to focus the discussion on
pacemaker_remote, and to be able to use a single physical host in the example.
Now, the status output should look similar to this:
# pcs status Cluster name: mycluster Stack: corosync Current DC: example-host (version 1.1.16-12.el7_4.5-94ff4df) - partition with quorum Last updated: Fri Jan 12 15:22:49 2018 Last change: Fri Jan 12 15:22:46 2018 by root via cibadmin on example-host 1 node configured 0 resources configured Online: [ example-host ] No active resources Daemon Status: corosync: active/disabled pacemaker: active/disabled pcsd: active/enabled
Go ahead and stop the cluster for now after verifying everything is in order.
# pcs cluster stop --force
# yum install -y kvm libvirt qemu-system qemu-kvm bridge-utils virt-manager # systemctl enable libvirtd.service
Reboot the host.
Note
While KVM is used in this example, any virtualization platform with a Pacemaker resource agent can be used to create a guest node. The resource agent needs only to support usual commands (start, stop, etc.); Pacemaker implements the remote-node meta-attribute, independent of the agent.
We will not outline here the installation steps required to create a KVM guest. There are plenty of tutorials available elsewhere that do that. Just be sure to configure the guest with a hostname and a static IP address (as an example here, we will use guest1 and 192.168.122.10).
On each guest, allow cluster-related services through the local firewall, following the same procedure as in Configure Firewall on Host.
At this point, you should be able to ping and ssh into guests from hosts, and vice versa.
Install pacemaker_remote, and enable it to run at start-up. Here, we also install the pacemaker package; it is not required, but it contains the dummy resource agent that we will use later for testing.
# yum install -y pacemaker pacemaker-remote resource-agents # systemctl enable pacemaker_remote.service
Copy the authentication key from a host:
# mkdir -p --mode=0750 /etc/pacemaker # chgrp haclient /etc/pacemaker # scp root@example-host:/etc/pacemaker/authkey /etc/pacemaker
Start pacemaker_remote, and verify the start was successful:
# systemctl start pacemaker_remote
# systemctl status pacemaker_remote
pacemaker_remote.service - Pacemaker Remote Service
Loaded: loaded (/usr/lib/systemd/system/pacemaker_remote.service; enabled)
Active: active (running) since Thu 2013-03-14 18:24:04 EDT; 2min 8s ago
Main PID: 1233 (pacemaker_remot)
CGroup: name=systemd:/system/pacemaker_remote.service
└─1233 /usr/sbin/pacemaker-remoted
Mar 14 18:24:04 guest1 systemd[1]: Starting Pacemaker Remote Service...
Mar 14 18:24:04 guest1 systemd[1]: Started Pacemaker Remote Service.
Mar 14 18:24:04 guest1 pacemaker-remoted[1233]: notice: lrmd_init_remote_tls_server: Starting a tls listener on port 3121.
Before moving forward, it's worth verifying that the host can contact the guest on port 3121. Here's a trick you can use. Connect using ssh from the host. The connection will get destroyed, but how it is destroyed tells you whether it worked or not.
First add guest1 to the host machine's +/etc/hosts+ file if you haven't already. This is required unless you have DNS setup in a way where guest1's address can be discovered.
# cat << END >> /etc/hosts 192.168.122.10 guest1 END
If running the ssh command on one of the cluster nodes results in this output before disconnecting, the connection works:
# ssh -p 3121 guest1 ssh_exchange_identification: read: Connection reset by peer
If you see one of these, the connection is not working:
# ssh -p 3121 guest1 ssh: connect to host guest1 port 3121: No route to host
# ssh -p 3121 guest1 ssh: connect to host guest1 port 3121: Connection refused
Once you can successfully connect to the guest from the host, shutdown the guest. Pacemaker will be managing the virtual machine from this point forward.
Now the fun part, integrating the virtual machine you've just created into the cluster. It is incredibly simple.
On the host, start pacemaker.
# pcs cluster start
Wait for the host to become the DC. The output of pcs status should look
as it did in Disable Stonith and Quorum.
If you didn't already do this earlier in the verify host to guest connection
section, add the KVM guest's IP address to the host's /etc/hosts file so we
can connect by hostname. For this example:
# cat << END >> /etc/hosts 192.168.122.10 guest1 END
We will use the VirtualDomain resource agent for the management of the virtual machine. This agent requires the virtual machine's XML config to be dumped to a file on disk. To do this, pick out the name of the virtual machine you just created from the output of this list.
# virsh list --all Id Name State ---------------------------------------------------- - guest1 shut off
In my case I named it guest1. Dump the xml to a file somewhere on the host using the following command.
# virsh dumpxml guest1 > /etc/pacemaker/guest1.xml
Now just register the resource with pacemaker and you're set!
# pcs resource create vm-guest1 VirtualDomain hypervisor="qemu:///system" \
config="/etc/pacemaker/guest1.xml" meta remote-node=guest1
Note
This example puts the guest XML under /etc/pacemaker because the
permissions and SELinux labeling should not need any changes.
If you run into trouble with this or any step, try disabling SELinux
with setenforce 0. If it works after that, see SELinux documentation
for how to troubleshoot, if you wish to reenable SELinux.
Note
Pacemaker will automatically monitor pacemaker_remote connections for failure, so it is not necessary to create a recurring monitor on the VirtualDomain resource.
Once the vm-guest1 resource is started you will see guest1 appear in the
pcs status output as a node. The final pcs status output should look
something like this.
# pcs status Cluster name: mycluster Stack: corosync Current DC: example-host (version 1.1.16-12.el7_4.5-94ff4df) - partition with quorum Last updated: Fri Jan 12 18:00:45 2018 Last change: Fri Jan 12 17:53:44 2018 by root via crm_resource on example-host 2 nodes configured 2 resources configured Online: [ example-host ] GuestOnline: [ guest1@example-host ] Full list of resources: vm-guest1 (ocf::heartbeat:VirtualDomain): Started example-host Daemon Status: corosync: active/disabled pacemaker: active/disabled pcsd: active/enabled
The commands below demonstrate how resources can be executed on both the guest node and the cluster node.
Create a few Dummy resources. Dummy resources are real resource agents used just for testing purposes. They actually execute on the host they are assigned to just like an apache server or database would, except their execution just means a file was created. When the resource is stopped, that the file it created is removed.
# pcs resource create FAKE1 ocf:pacemaker:Dummy # pcs resource create FAKE2 ocf:pacemaker:Dummy # pcs resource create FAKE3 ocf:pacemaker:Dummy # pcs resource create FAKE4 ocf:pacemaker:Dummy # pcs resource create FAKE5 ocf:pacemaker:Dummy
Now check your pcs status output. In the resource section, you should see
something like the following, where some of the resources started on the
cluster node, and some started on the guest node.
Full list of resources: vm-guest1 (ocf::heartbeat:VirtualDomain): Started example-host FAKE1 (ocf::pacemaker:Dummy): Started guest1 FAKE2 (ocf::pacemaker:Dummy): Started guest1 FAKE3 (ocf::pacemaker:Dummy): Started example-host FAKE4 (ocf::pacemaker:Dummy): Started guest1 FAKE5 (ocf::pacemaker:Dummy): Started example-host
The guest node, guest1, reacts just like any other node in the cluster. For example, pick out a resource that is running on your cluster node. For my purposes, I am picking FAKE3 from the output above. We can force FAKE3 to run on guest1 in the exact same way we would any other node.
# pcs constraint location FAKE3 prefers guest1
Now, looking at the bottom of the pcs status output you'll see FAKE3 is on guest1.
Full list of resources: vm-guest1 (ocf::heartbeat:VirtualDomain): Started example-host FAKE1 (ocf::pacemaker:Dummy): Started guest1 FAKE2 (ocf::pacemaker:Dummy): Started guest1 FAKE3 (ocf::pacemaker:Dummy): Started guest1 FAKE4 (ocf::pacemaker:Dummy): Started example-host FAKE5 (ocf::pacemaker:Dummy): Started example-host
Pacemaker's scheduler is smart enough to know fencing guest nodes associated with a virtual machine means shutting off/rebooting the virtual machine. No special configuration is necessary to make this happen. If you are interested in testing this functionality out, trying stopping the guest's pacemaker_remote daemon. This would be equivalent of abruptly terminating a cluster node's corosync membership without properly shutting it down.
ssh into the guest and run this command.
# kill -9 $(pidof pacemaker-remoted)
Within a few seconds, your pcs status output will show a monitor failure,
and the guest1 node will not be shown while it is being recovered.
# pcs status
Cluster name: mycluster
Stack: corosync
Current DC: example-host (version 1.1.16-12.el7_4.5-94ff4df) - partition with quorum
Last updated: Fri Jan 12 18:08:35 2018
Last change: Fri Jan 12 18:07:00 2018 by root via cibadmin on example-host
2 nodes configured
7 resources configured
Online: [ example-host ]
Full list of resources:
vm-guest1 (ocf::heartbeat:VirtualDomain): Started example-host
FAKE1 (ocf::pacemaker:Dummy): Stopped
FAKE2 (ocf::pacemaker:Dummy): Stopped
FAKE3 (ocf::pacemaker:Dummy): Stopped
FAKE4 (ocf::pacemaker:Dummy): Started example-host
FAKE5 (ocf::pacemaker:Dummy): Started example-host
Failed Actions:
* guest1_monitor_30000 on example-host 'unknown error' (1): call=8, status=Error, exitreason='none',
last-rc-change='Fri Jan 12 18:08:29 2018', queued=0ms, exec=0ms
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
Note
A guest node involves two resources: the one you explicitly configured creates the guest, and Pacemaker creates an implicit resource for the pacemaker_remote connection, which will be named the same as the value of the remote-node attribute of the explicit resource. When we killed pacemaker_remote, it is the implicit resource that failed, which is why the failed action starts with guest1 and not vm-guest1.
Once recovery of the guest is complete, you'll see it automatically get
re-integrated into the cluster. The final pcs status output should look
something like this.
Cluster name: mycluster
Stack: corosync
Current DC: example-host (version 1.1.16-12.el7_4.5-94ff4df) - partition with quorum
Last updated: Fri Jan 12 18:18:30 2018
Last change: Fri Jan 12 18:07:00 2018 by root via cibadmin on example-host
2 nodes configured
7 resources configured
Online: [ example-host ]
GuestOnline: [ guest1@example-host ]
Full list of resources:
vm-guest1 (ocf::heartbeat:VirtualDomain): Started example-host
FAKE1 (ocf::pacemaker:Dummy): Started guest1
FAKE2 (ocf::pacemaker:Dummy): Started guest1
FAKE3 (ocf::pacemaker:Dummy): Started guest1
FAKE4 (ocf::pacemaker:Dummy): Started example-host
FAKE5 (ocf::pacemaker:Dummy): Started example-host
Failed Actions:
* guest1_monitor_30000 on example-host 'unknown error' (1): call=8, status=Error, exitreason='none',
last-rc-change='Fri Jan 12 18:08:29 2018', queued=0ms, exec=0ms
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
Normally, once you've investigated and addressed a failed action, you can clear the failure. However Pacemaker does not yet support cleanup for the implicitly created connection resource while the explicit resource is active. If you want to clear the failed action from the status output, stop the guest resource before clearing it. For example:
# pcs resource disable vm-guest1 --wait # pcs resource cleanup guest1 # pcs resource enable vm-guest1
Besides allowing the cluster to manage resources on a guest node,
pacemaker_remote has one other trick. The pacemaker_remote daemon allows
nearly all the pacemaker tools (crm_resource, crm_mon, crm_attribute,
crm_master, etc.) to work on guest nodes natively.
Try it: Run crm_mon on the guest after pacemaker has
integrated the guest node into the cluster. These tools just work. This
means resource agents such as promotable resources (which need access to tools
like crm_master) work seamlessly on the guest nodes.
Higher-level command shells such as pcs may have partial support
on guest nodes, but it is recommended to run them from a cluster node.