Remote Node Walk-through

Updated 108 Days AgoPublic

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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.

This tutorial uses a RHEL-like OS as an example, using pcs as a higher-level tool. The concepts apply to other distros and tools, but the exact syntax might differ.

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.

Configure Remote Node

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

# setenforce 0
# sed -i.bak "s/SELINUX=enforcing/SELINUX=permissive/g" /etc/selinux/config
# systemctl mask firewalld.service
# systemctl stop firewalld.service

Configure hostname resolution

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

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

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

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

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

Starting Resources on a 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.

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.

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.

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; for example, 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.