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.. index::
single: guest node; walk-through
Guest Node Walk-through
-----------------------
**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.
Configure Cluster Nodes
#######################
This walk-through assumes you already have a Pacemaker cluster configured. For examples, we will use a cluster with two cluster nodes named pcmk-1 and pcmk-2. You can substitute whatever your node names are, for however many nodes you have. If you are not familiar with setting up basic Pacemaker clusters, follow the walk-through in the Clusters From Scratch document before attempting this one.
Install Virtualization Software
_______________________________
On each node within your cluster, install virt-install, libvirt, and qemu-kvm.
Start and enable ``virtnetworkd``.
.. code-block:: none
# dnf install -y virt-install libvirt qemu-kvm
# systemctl start virtnetworkd
# systemctl enable virtnetworkd
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.
Configure the KVM guest
#######################
Create Guest
____________
Create a KVM guest to use as a guest node. 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).
Here's an example way to create a guest:
* Download an .iso file from the |REMOTE_DISTRO| |REMOTE_DISTRO_VER| `mirrors
list <https://mirrors.almalinux.org/isos.html>`_ into a directory on your
cluster node.
* Run the following command, using your own path for the **location** flag:
.. code-block:: none
[root@pcmk-1 ~]# virt-install \
--name vm-guest1 \
--memory 1536 \
--disk path=/var/lib/libvirt/images/vm-guest1.qcow2,size=4 \
--vcpus 2 \
--os-variant almalinux9 \
--network bridge=virbr0 \
--graphics none \
--console pty,target_type=serial \
--location /tmp/AlmaLinux-9-latest-x86_64-dvd.iso \
--extra-args 'console=ttyS0,115200n8'
.. NOTE::
See the Clusters from Scratch document for more details about installing
|REMOTE_DISTRO| |REMOTE_DISTRO_VER|. The above command will perform a
text-based installation by default, but feel free to do a graphical
installation, which exposes more options.
.. index::
single: guest node; firewall
Configure Firewall on Guest
___________________________
On each guest, allow cluster-related services through the local firewall. If
you're using ``firewalld``, run the following commands.
.. code-block:: none
[root@guest1 ~]# firewall-cmd --permanent --add-service=high-availability
success
[root@guest1 ~]# firewall-cmd --reload
success
.. NOTE::
If you are using 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.
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:
.. code-block:: none
[root@guest1 ~]# setenforce 0
[root@guest1 ~]# sed -i.bak "s/SELINUX=enforcing/SELINUX=permissive/g" \
/etc/selinux/config
[root@guest1 ~]# systemctl mask firewalld.service
[root@guest1 ~]# systemctl stop firewalld.service
Configure ``/etc/hosts``
________________________
You will need to add the remote node's hostname (we're using **guest1** in
this tutorial) to the cluster nodes' ``/etc/hosts`` files if you haven't already.
This is required unless you have DNS set up in a way where guest1's address can be
discovered.
For each guest, execute the following on each cluster node and on the guests,
replacing the IP address with the actual IP address of the guest node.
.. code-block:: none
# cat << END >> /etc/hosts
192.168.122.10 guest1
END
Also add entries for each cluster node to the ``/etc/hosts`` file on each guest.
For example:
.. code-block:: none
# cat << END >> /etc/hosts
192.168.122.101 pcmk-1
192.168.122.102 pcmk-2
END
Verify Connectivity
___________________
At this point, you should be able to ping and ssh into guests from hosts, and
vice versa.
Depending on your installation method, you may have to perform an additional
step to make SSH work. The simplest approach is to open the
``/etc/ssh/sshd_config`` file and set ``PermitRootLogin yes``. Then to make the
change take effect, run the following command.
.. code-block:: none
[root@guest1 ~]# systemctl restart sshd
Configure pacemaker_remote on Guest Node
________________________________________
Install the pacemaker_remote daemon on the guest node. We'll also install the
``pacemaker`` package. It isn't required for a guest node to run, but it
provides the ``crm_attribute`` tool, which many resource agents use.
.. code-block:: none
[root@guest1 ~]# dnf config-manager --set-enabled highavailability
[root@guest1 ~]# dnf install -y pacemaker-remote resource-agents pcs \
pacemaker
Integrate Guest into Cluster
############################
Now the fun part, integrating the virtual machine you've just created into the
cluster. It is incredibly simple.
Start the Cluster
_________________
On the host, start Pacemaker if it's not already running.
.. code-block:: none
# pcs cluster start
Create a ``VirtualDomain`` Resource for the Guest VM
____________________________________________________
For this simple walk-through, we have created the VM and made its disk
available only on node ``pcmk-1``, so that's the only node where the VM is
capable of running. In a more realistic scenario, you'll probably want to have
multiple nodes that are capable of running the VM.
Next we'll assign an attribute to node 1 that denotes its eligibility to host
``vm-guest1``. If other nodes are capable of hosting your guest VM, then add the
attribute to each of those nodes as well.
.. code-block:: none
[root@pcmk-1 ~]# pcs node attribute pcmk-1 can-host-vm-guest1=1
Then we'll create a ``VirtualDomain`` resource so that Pacemaker can manage
``vm-guest1``. Be sure to replace the XML file path below with your own if it
differs. We'll also create a rule to prevent Pacemaker from trying to start the
resource or probe its status on any node that isn't capable of running the VM.
We'll save the CIB to a file, make both of these edits, and push them
simultaneously.
.. code-block:: none
[root@pcmk-1 ~]# pcs cluster cib vm_cfg
[root@pcmk-1 ~]# pcs -f vm_cfg resource create vm-guest1 VirtualDomain \
hypervisor="qemu:///system" config="/etc/libvirt/qemu/vm-guest1.xml"
Assumed agent name 'ocf:heartbeat:VirtualDomain' (deduced from 'VirtualDomain')
[root@pcmk-1 ~]# pcs -f vm_cfg constraint location vm-guest1 rule \
resource-discovery=never score=-INFINITY can-host-vm-guest1 ne 1
[root@pcmk-1 ~]# pcs cluster cib-push --config vm_cfg --wait
.. NOTE::
If all nodes in your cluster are capable of hosting the VM that you've
created, then you can skip the ``pcs node attribute`` and ``pcs constraint
location`` commands.
.. NOTE::
The ID of the resource managing the virtual machine (``vm-guest1`` in the
above example) **must** be different from the virtual machine's node name
(``guest1`` in the above example). Pacemaker will create an implicit
internal resource for the Pacemaker Remote connection to the guest. This
implicit resource will be named with the value of the ``VirtualDomain``
resource's ``remote-node`` meta attribute, which will be set by ``pcs`` to
the guest node's node name. Therefore, that value cannot be used as the name
of any other resource.
Now we can confirm that the ``VirtualDomain`` resource is running on ``pcmk-1``.
.. code-block:: none
[root@pcmk-1 ~]# pcs resource status
* vm-guest1 (ocf:heartbeat:VirtualDomain): Started pcmk-1
Prepare ``pcsd``
________________
Now we need to prepare ``pcsd`` on the guest so that we can use ``pcs`` commands
to communicate with it.
Start and enable the ``pcsd`` daemon on the guest.
.. code-block:: none
[root@guest1 ~]# systemctl start pcsd
[root@guest1 ~]# systemctl enable pcsd
Created symlink /etc/systemd/system/multi-user.target.wants/pcsd.service → /usr/lib/systemd/system/pcsd.service.
Next, set a password for the |CRM_DAEMON_USER| user on the guest.
.. code-block:: none
[root@guest1 ~]# echo MyPassword | passwd --stdin hacluster
Changing password for user hacluster.
passwd: all authentication tokens updated successfully.
Now authenticate the existing cluster nodes to ``pcsd`` on the guest. The below
command only needs to be run from one cluster node.
.. code-block:: none
[root@pcmk-1 ~]# pcs host auth guest1 -u hacluster
Password:
guest1: Authorized
Integrate Guest Node into Cluster
_________________________________
We're finally ready to integrate the VM into the cluster as a guest node. Run
the following command, which will create a guest node from the ``VirtualDomain``
resource and take care of all the remaining steps. Note that the format is ``pcs
cluster node add-guest <guest_name> <vm_resource_name>``.
.. code-block:: none
[root@pcmk-1 ~]# pcs cluster node add-guest guest1 vm-guest1
No addresses specified for host 'guest1', using 'guest1'
Sending 'pacemaker authkey' to 'guest1'
guest1: successful distribution of the file 'pacemaker authkey'
Requesting 'pacemaker_remote enable', 'pacemaker_remote start' on 'guest1'
guest1: successful run of 'pacemaker_remote enable'
guest1: successful run of 'pacemaker_remote start'
You should soon see ``guest1`` appear in the ``pcs status`` output as a node.
The output should look something like this:
.. code-block:: none
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Cluster Summary:
* Stack: corosync
* Current DC: pcmk-1 (version 2.1.2-4.el9-ada5c3b36e2) - partition with quorum
* Last updated: Wed Aug 10 00:08:58 2022
* Last change: Wed Aug 10 00:02:37 2022 by root via cibadmin on pcmk-1
* 3 nodes configured
* 3 resource instances configured
Node List:
* Online: [ pcmk-1 pcmk-2 ]
* GuestOnline: [ guest1@pcmk-1 ]
Full List of Resources:
* xvm (stonith:fence_xvm): Started pcmk-1
* vm-guest1 (ocf:heartbeat:VirtualDomain): Started pcmk-1
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
The resulting configuration should look something like the following:
.. code-block:: none
[root@pcmk-1 ~]# pcs resource config
Resource: vm-guest1 (class=ocf provider=heartbeat type=VirtualDomain)
Attributes: config=/etc/libvirt/qemu/vm-guest1.xml hypervisor=qemu:///system
Meta Attrs: remote-addr=guest1 remote-node=guest1
Operations: migrate_from interval=0s timeout=60s (vm-guest1-migrate_from-interval-0s)
migrate_to interval=0s timeout=120s (vm-guest1-migrate_to-interval-0s)
monitor interval=10s timeout=30s (vm-guest1-monitor-interval-10s)
start interval=0s timeout=90s (vm-guest1-start-interval-0s)
stop interval=0s timeout=90s (vm-guest1-stop-interval-0s)
How pcs Configures the Guest
____________________________
Let's take a closer look at what the ``pcs cluster node add-guest`` command is
doing. There is no need to run any of the commands in this section.
First, ``pcs`` copies the Pacemaker authkey file to the VM that will become the
guest. If an authkey is not already present on the cluster nodes, this command
creates one and distributes it to the existing nodes and to the guest.
If you want to do this manually, you can run a command like the following to
generate an authkey in ``/etc/pacemaker/authkey``, and then distribute the key
to the rest of the nodes and to the new guest.
.. code-block:: none
[root@pcmk-1 ~]# dd if=/dev/urandom of=/etc/pacemaker/authkey bs=4096 count=1
Then ``pcs`` starts and enables the ``pacemaker_remote`` service on the guest.
If you want to do this manually, run the following commands.
.. code-block:: none
[root@guest1 ~]# systemctl start pacemaker_remote
[root@guest1 ~]# systemctl enable pacemaker_remote
Finally, ``pcs`` creates a guest node from the ``VirtualDomain`` resource by
adding ``remote-addr`` and ``remote-node`` meta attributes to the resource. If
you want to do this manually, you can run the following command if you're using
``pcs``. Alternativately, run an equivalent command if you're using another
cluster shell, or edit the CIB manually.
.. code-block:: none
[root@pcmk-1 ~]# pcs resource update vm-guest1 meta remote-addr='guest1' \
remote-node='guest1' --force
Starting Resources on KVM Guest
###############################
The following example demonstrates that resources can be run on the guest node
in the exact same way as on the cluster nodes.
Create a few ``Dummy`` resources. A ``Dummy`` resource is a real resource that
actually executes operations on its assigned node. However, these operations are
trivial (creating, deleting, or checking the existence of an empty or small
file), so ``Dummy`` resources are ideal for testing purposes. ``Dummy``
resources use the ``ocf:heartbeat:Dummy`` or ``ocf:pacemaker:Dummy`` resource
agent.
.. code-block:: none
# for i in {1..5}; do pcs resource create FAKE${i} ocf:heartbeat:Dummy; done
Now run ``pcs resource status``. You should see something like the following,
where some of the resources are started on the cluster nodes, and some are
started on the guest node.
.. code-block:: none
[root@pcmk-1 ~]# pcs resource status
* vm-guest1 (ocf:heartbeat:VirtualDomain): Started pcmk-1
* FAKE1 (ocf:heartbeat:Dummy): Started guest1
* FAKE2 (ocf:heartbeat:Dummy): Started pcmk-2
* FAKE3 (ocf:heartbeat:Dummy): Started guest1
* FAKE4 (ocf:heartbeat:Dummy): Started pcmk-2
* FAKE5 (ocf:heartbeat:Dummy): Started guest1
The guest node, ``guest1``, behaves just like any other node in the cluster with
respect to resources. For example, choose a resource that is running on one of
your cluster nodes. We'll choose ``FAKE2`` from the output above. It's currently
running on ``pcmk-2``. We can force ``FAKE2`` to run on ``guest1`` in the exact
same way as we could force it to run on any particular cluster node. We do this
by creating a location constraint:
.. code-block:: none
# pcs constraint location FAKE2 prefers guest1
Now the ``pcs resource status`` output shows that ``FAKE2`` is on ``guest1``.
.. code-block:: none
[root@pcmk-1 ~]# pcs resource status
* vm-guest1 (ocf:heartbeat:VirtualDomain): Started pcmk-1
* FAKE1 (ocf:heartbeat:Dummy): Started guest1
* FAKE2 (ocf:heartbeat:Dummy): Started guest1
* FAKE3 (ocf:heartbeat:Dummy): Started guest1
* FAKE4 (ocf:heartbeat:Dummy): Started pcmk-2
* FAKE5 (ocf:heartbeat:Dummy): Started guest1
Testing Recovery and Fencing
############################
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.
.. code-block:: none
[root@guest1 ~]# 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.
.. code-block:: none
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Cluster Summary:
* Stack: corosync
* Current DC: pcmk-1 (version 2.1.2-4.el9-ada5c3b36e2) - partition with quorum
* Last updated: Wed Aug 10 01:39:40 2022
* Last change: Wed Aug 10 01:34:55 2022 by root via cibadmin on pcmk-1
* 3 nodes configured
* 8 resource instances configured
Node List:
* Online: [ pcmk-1 pcmk-2 ]
Full List of Resources:
* xvm (stonith:fence_xvm): Started pcmk-1
* vm-guest1 (ocf:heartbeat:VirtualDomain): FAILED pcmk-1
* FAKE1 (ocf:heartbeat:Dummy): FAILED guest1
* FAKE2 (ocf:heartbeat:Dummy): FAILED guest1
* FAKE3 (ocf:heartbeat:Dummy): FAILED guest1
* FAKE4 (ocf:heartbeat:Dummy): Started pcmk-2
* FAKE5 (ocf:heartbeat:Dummy): FAILED guest1
Failed Resource Actions:
* guest1 30s-interval monitor on pcmk-1 could not be executed (Error) because 'Lost connection to remote executor' at Wed Aug 10 01:39:38 2022
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
.. NOTE::
A guest node involves two resources: an explicitly configured resource that
you create, which manages the virtual machine (the ``VirtualDomain``
resource in our example); and an implicit resource that Pacemaker creates,
which manages the ``pacemaker-remoted`` connection to the guest. The
implicit resource's name is the value of the explicit resource's
``remote-node`` meta attribute. When we killed ``pacemaker-remoted``, the
**implicit** resource is what failed. That's 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.
.. code-block:: none
[root@pcmk-1 ~]# pcs status
Cluster name: mycluster
Cluster Summary:
* Stack: corosync
* Current DC: pcmk-1 (version 2.1.2-4.el9-ada5c3b36e2) - partition with quorum
* Last updated: Wed Aug 10 01:40:05 2022
* Last change: Wed Aug 10 01:34:55 2022 by root via cibadmin on pcmk-1
* 3 nodes configured
* 8 resource instances configured
Node List:
* Online: [ pcmk-1 pcmk-2 ]
* GuestOnline: [ guest1@pcmk-1 ]
Full List of Resources:
* xvm (stonith:fence_xvm): Started pcmk-1
* vm-guest1 (ocf:heartbeat:VirtualDomain): Started pcmk-1
* FAKE1 (ocf:heartbeat:Dummy): Started guest1
* FAKE2 (ocf:heartbeat:Dummy): Started guest1
* FAKE3 (ocf:heartbeat:Dummy): Started pcmk-2
* FAKE4 (ocf:heartbeat:Dummy): Started pcmk-2
* FAKE5 (ocf:heartbeat:Dummy): Started guest1
Failed Resource Actions:
* guest1 30s-interval monitor on pcmk-1 could not be executed (Error) because 'Lost connection to remote executor' at Wed Aug 10 01:39:38 2022
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:
.. code-block:: none
# pcs resource disable vm-guest1 --wait
# pcs resource cleanup guest1
# pcs resource enable vm-guest1
Accessing Cluster Tools from Guest Node
#######################################
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``,
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_attribute``) 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.
Troubleshooting a Remote Connection
###################################
If connectivity issues occur, it's worth verifying that the cluster nodes can
communicate with the guest node on TCP port 3121. We can use the ``nc`` command
to test the connection.
On the cluster nodes, install the package that provides the ``nc`` command. The
package name may vary by distribution; on |REMOTE_DISTRO| |REMOTE_DISTRO_VER|
it's ``nmap-ncat``.
Now connect using ``nc`` from each of the cluster nodes to the guest and run a
``/bin/true`` command that does nothing except return success. No output
indicates that the cluster node is able to communicate with the guest on TCP
port 3121. An error indicates that the connection failed. This could be due to
a network issue or because ``pacemaker-remoted`` is not currently running on
the guest node.
Example of success:
.. code-block:: none
[root@pcmk-1 ~]# nc guest1 3121 --sh-exec /bin/true
[root@pcmk-1 ~]#
Examples of failure:
.. code-block:: none
[root@pcmk-1 ~]# nc guest1 3121 --sh-exec /bin/true
Ncat: Connection refused.
[root@pcmk-1 ~]# nc guest1 3121 --sh-exec /bin/true
Ncat: No route to host.

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