4. Remote Node Walk-through¶
What this tutorial is: An in-depth walk-through of how to get Pacemaker to integrate a remote node into the cluster as a node capable of running cluster resources.
What this tutorial is not: A realistic deployment scenario. The steps shown here are meant to get users familiar with the concept of remote nodes as quickly as possible.
4.1. 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.
4.2. Configure Remote Node¶
4.2.1. Configure Firewall on Remote Node¶
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 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:
# setenforce 0
# sed -i.bak "s/SELINUX=enforcing/SELINUX=permissive/g" \
/etc/selinux/config
# systemctl mask firewalld.service
# systemctl stop firewalld.service
4.2.2. Configure /etc/hosts¶
You will need to add the remote node’s hostname (we’re using remote1 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 remote1’s address can be
discovered.
For each remote node, execute the following on each cluster node and on the remote nodes, replacing the IP address with the actual IP address of the remote node.
# cat << END >> /etc/hosts
192.168.122.10 remote1
END
Also add entries for each cluster node to the /etc/hosts file on each
remote node. For example:
# cat << END >> /etc/hosts
192.168.122.101 pcmk-1
192.168.122.102 pcmk-2
END
4.2.3. Configure pacemaker_remote on Remote Node¶
Install the pacemaker_remote daemon on the remote node.
[root@remote1 ~]# dnf config-manager --set-enabled highavailability
[root@remote1 ~]# dnf install -y pacemaker-remote resource-agents pcs
4.2.4. Prepare pcsd¶
Now we need to prepare pcsd on the remote node so that we can use pcs
commands to communicate with it.
Start and enable the pcsd daemon on the remote node.
[root@remote1 ~]# systemctl start pcsd
[root@remote1 ~]# 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 hacluster user on the remote node
[root@remote ~]# 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 remote node. The
below command only needs to be run from one cluster node.
[root@pcmk-1 ~]# pcs host auth remote1 -u hacluster
Password:
remote1: Authorized
4.2.5. Integrate Remote Node into Cluster¶
Integrating a remote node into the cluster is achieved through the
creation of a remote node connection resource. The remote node connection
resource both establishes the connection to the remote node and defines that
the remote node exists. Note that this resource is actually internal to
Pacemaker’s controller. The metadata for this resource can be found in
the /usr/lib/ocf/resource.d/pacemaker/remote file. The metadata in this file
describes what options are available, but there is no actual
ocf:pacemaker:remote resource agent script that performs any work.
Define the remote node connection resource to our remote node,
remote1, using the following command on any cluster node. This
command creates the ocf:pacemaker:remote resource; creates the authkey if it
does not exist already and distributes it to the remote node; and starts and
enables pacemaker-remoted on the remote node.
[root@pcmk-1 ~]# pcs cluster node add-remote remote1
No addresses specified for host 'remote1', using 'remote1'
Sending 'pacemaker authkey' to 'remote1'
remote1: successful distribution of the file 'pacemaker authkey'
Requesting 'pacemaker_remote enable', 'pacemaker_remote start' on 'remote1'
remote1: successful run of 'pacemaker_remote enable'
remote1: successful run of 'pacemaker_remote start'
That’s it. After a moment you should see the remote node come online. The final pcs status output should look something like this, and you can see that it
created the ocf:pacemaker:remote resource:
[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 05:17:28 2022
* Last change: Wed Aug 10 05:17:26 2022 by root via cibadmin on pcmk-1
* 3 nodes configured
* 2 resource instances configured
Node List:
* Online: [ pcmk-1 pcmk-2 ]
* RemoteOnline: [ remote1 ]
Full List of Resources:
* xvm (stonith:fence_xvm): Started pcmk-1
* remote1 (ocf:pacemaker:remote): Started pcmk-1
Daemon Status:
corosync: active/disabled
pacemaker: active/disabled
pcsd: active/enabled
4.3. How pcs Configures the Remote¶
Let’s take a closer look at what the pcs cluster node add-remote 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.
[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.
[root@guest1 ~]# systemctl start pacemaker_remote
[root@guest1 ~]# systemctl enable pacemaker_remote
4.4. Starting Resources on Remote Node¶
Once the remote node is integrated into the cluster, starting and managing resources on a remote node is the exact same as on cluster nodes. Refer to the Clusters from Scratch document for examples of resource creation.
Warning
Never involve a remote node connection resource in a resource group, colocation constraint, or order constraint.
4.5. Fencing Remote Nodes¶
Remote nodes are fenced the same way as cluster nodes. No special considerations are required. Configure fencing resources for use with remote nodes the same as you would with cluster nodes.
Note, however, that remote nodes can never ‘initiate’ a fencing action. Only cluster nodes are capable of actually executing a fencing operation against another node.
4.6. Accessing Cluster Tools from a Remote Node¶
Besides allowing the cluster to manage resources on a remote 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 remote nodes natively.
Try it: Run crm_mon on the remote node after pacemaker has
integrated it into the cluster. These tools just work. These means resource
agents such as promotable resources (which need access to tools like
crm_attribute) work seamlessly on the remote nodes.
Higher-level command shells such as pcs may have partial support
on remote nodes, but it is recommended to run them from a cluster node.
4.7. Troubleshooting a Remote Connection¶
If connectivity issues occur, it’s worth verifying that the cluster nodes can
communicate with the remote 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 AlmaLinux 9
it’s nmap-ncat.
Now connect using nc from each of the cluster nodes to the remote node 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 remote node 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 remote node.
Example of success:
[root@pcmk-1 ~]# nc remote1 3121 --sh-exec /bin/true
[root@pcmk-1 ~]#
Examples of failure:
[root@pcmk-1 ~]# nc remote1 3121 --sh-exec /bin/true
Ncat: Connection refused.
[root@pcmk-1 ~]# nc remote1 3121 --sh-exec /bin/true
Ncat: No route to host.