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Chapter 29. Integrating non-corosync nodes into a cluster: the pacemaker_remote service
pacemaker_remote service allows nodes not running
corosync to integrate into the cluster and have the cluster manage their resources just as if they were real cluster nodes.
Among the capabilities that the
pacemaker_remote service provides are the following:
pacemaker_remoteservice allows you to scale beyond the Red Hat support limit of 32 nodes for RHEL 8.1.
pacemaker_remoteservice allows you to manage a virtual environment as a cluster resource and also to manage individual services within the virtual environment as cluster resources.
The following terms are used to describe the
cluster node — A node running the High Availability services (
remote node — A node running
pacemaker_remoteto remotely integrate into the cluster without requiring
corosynccluster membership. A remote node is configured as a cluster resource that uses the
guest node — A virtual guest node running the
pacemaker_remoteservice. The virtual guest resource is managed by the cluster; it is both started by the cluster and integrated into the cluster as a remote node.
pacemaker_remote — A service daemon capable of performing remote application management within remote nodes and KVM guest nodes in a Pacemaker cluster environment. This service is an enhanced version of Pacemaker’s local executor daemon (
pacemaker-execd) that is capable of managing resources remotely on a node not running corosync.
A Pacemaker cluster running the
pacemaker_remote service has the following characteristics.
Remote nodes and guest nodes run the
pacemaker_remoteservice (with very little configuration required on the virtual machine side).
The cluster stack (
corosync), running on the cluster nodes, connects to the
pacemaker_remoteservice on the remote nodes, allowing them to integrate into the cluster.
The cluster stack (
corosync), running on the cluster nodes, launches the guest nodes and immediately connects to the
pacemaker_remoteservice on the guest nodes, allowing them to integrate into the cluster.
The key difference between the cluster nodes and the remote and guest nodes that the cluster nodes manage is that the remote and guest nodes are not running the cluster stack. This means the remote and guest nodes have the following limitations:
- they do not take place in quorum
- they do not execute fencing device actions
- they are not eligible to be the cluster’s Designated Controller (DC)
they do not themselves run the full range of
On the other hand, remote nodes and guest nodes are not bound to the scalability limits associated with the cluster stack.
Other than these noted limitations, the remote and guest nodes behave just like cluster nodes in respect to resource management, and the remote and guest nodes can themselves be fenced. The cluster is fully capable of managing and monitoring resources on each remote and guest node: You can build constraints against them, put them in standby, or perform any other action you perform on cluster nodes with the
pcs commands. Remote and guest nodes appear in cluster status output just as cluster nodes do.
29.1. Host and guest authentication of pacemaker_remote nodes
The connection between cluster nodes and pacemaker_remote is secured using Transport Layer Security (TLS) with pre-shared key (PSK) encryption and authentication over TCP (using port 3121 by default). This means both the cluster node and the node running
pacemaker_remote must share the same private key. By default this key must be placed at
/etc/pacemaker/authkey on both cluster nodes and remote nodes.
pcs cluster node add-guest command sets up the
authkey for guest nodes and the
pcs cluster node add-remote command sets up the
authkey for remote nodes.
29.2. Configuring KVM guest nodes
A Pacemaker guest node is a virtual guest node running the
pacemaker_remote service. The virtual guest node is managed by the cluster.
29.2.1. Guest node resource options
When configuring a virtual machine to act as a guest node, you create a
VirtualDomain resource, which manages the virtual machine. For descriptions of the options you can set for a
VirtualDomain resource, see the "Resource Options for Virtual Domain Resources" table in Virtual domain resource options.
In addition to the
VirtualDomain resource options, metadata options define the resource as a guest node and define the connection parameters. You set these resource options with the
pcs cluster node add-guest command. The following table describes these metadata options.
Table 29.1. Metadata Options for Configuring KVM Resources as Remote Nodes
| || |
The name of the guest node this resource defines. This both enables the resource as a guest node and defines the unique name used to identify the guest node. WARNING: This value cannot overlap with any resource or node IDs.
| || |
Configures a custom port to use for the guest connection to
| || |
The address provided in the
The IP address or host name to connect to
| || |
Amount of time before a pending guest connection will time out
29.2.2. Integrating a virtual machine as a guest node
The following procedure is a high-level summary overview of the steps to perform to have Pacemaker launch a virtual machine and to integrate that machine as a guest node, using
libvirt and KVM virtual guests.
Enter the following commands on every virtual machine to install
pacemaker_remotepackages, start the
pcsdservice and enable it to run on startup, and allow TCP port 3121 through the firewall.
# yum install pacemaker-remote resource-agents pcs # systemctl start pcsd.service # systemctl enable pcsd.service # firewall-cmd --add-port 3121/tcp --permanent # firewall-cmd --add-port 2224/tcp --permanent # firewall-cmd --reload
- Give each virtual machine a static network address and unique host name, which should be known to all nodes.
If you have not already done so, authenticate
pcsto the node you will be integrating as a quest node.
# pcs host auth nodename
Use the following command to convert an existing
VirtualDomainresource into a guest node. This command must be run on a cluster node and not on the guest node which is being added. In addition to converting the resource, this command copies the
/etc/pacemaker/authkeyto the guest node and starts and enables the
pacemaker_remotedaemon on the guest node. The node name for the guest node, which you can define arbitrarily, can differ from the host name for the node.
# pcs cluster node add-guest nodename resource_id [options]
After creating the
VirtualDomainresource, you can treat the guest node just as you would treat any other node in the cluster. For example, you can create a resource and place a resource constraint on the resource to run on the guest node as in the following commands, which are run from a cluster node. You can include guest nodes in groups, which allows you to group a storage device, file system, and VM.
# pcs resource create webserver apache configfile=/etc/httpd/conf/httpd.conf op monitor interval=30s # pcs constraint location webserver prefers nodename
29.3. Configuring Pacemaker remote nodes
A remote node is defined as a cluster resource with
ocf:pacemaker:remote as the resource agent. You create this resource with the
pcs cluster node add-remote command.
29.3.1. Remote node resource options
The following table describes the resource options you can configure for a
Table 29.2. Resource Options for Remote Nodes
| || |
Time in seconds to wait before attempting to reconnect to a remote node after an active connection to the remote node has been severed. This wait is recurring. If reconnect fails after the wait period, a new reconnect attempt will be made after observing the wait time. When this option is in use, Pacemaker will keep attempting to reach out and connect to the remote node indefinitely after each wait interval.
| || |
Address specified with
Server to connect to. This can be an IP address or host name.
| || |
TCP port to connect to.
29.3.2. Remote node configuration overview
The following procedure provides a high-level summary overview of the steps to perform to configure a Pacemaker Remote node and to integrate that node into an existing Pacemaker cluster environment.
On the node that you will be configuring as a remote node, allow cluster-related services through the local firewall.
# firewall-cmd --permanent --add-service=high-availability success # firewall-cmd --reload successNote
If you are using
iptablesdirectly, or some other firewall solution besides
firewalld, simply open the following ports: TCP ports 2224 and 3121.
pacemaker_remotedaemon on the remote node.
# yum install -y pacemaker-remote resource-agents pcs
Start and enable
pcsdon the remote node.
# systemctl start pcsd.service # systemctl enable pcsd.service
If you have not already done so, authenticate
pcsto the node you will be adding as a remote node.
# pcs host auth remote1
Add the remote node resource to the cluster with the following command. This command also syncs all relevant configuration files to the new node, starts the node, and configures it to start
pacemaker_remoteon boot. This command must be run on a cluster node and not on the remote node which is being added.
# pcs cluster node add-remote remote1
After adding the
remoteresource to the cluster, you can treat the remote node just as you would treat any other node in the cluster. For example, you can create a resource and place a resource constraint on the resource to run on the remote node as in the following commands, which are run from a cluster node.
# pcs resource create webserver apache configfile=/etc/httpd/conf/httpd.conf op monitor interval=30s # pcs constraint location webserver prefers remote1Warning
Never involve a remote node connection resource in a resource group, colocation constraint, or order constraint.
- Configure fencing resources for the remote node. Remote nodes are fenced the same way as cluster nodes. 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.
29.4. Changing the default port location
If you need to change the default port location for either Pacemaker or
pacemaker_remote, you can set the
PCMK_remote_port environment variable that affects both of these daemons. This environment variable can be enabled by placing it in the
/etc/sysconfig/pacemaker file as follows.
\#==#==# Pacemaker Remote ... # # Specify a custom port for Pacemaker Remote connections PCMK_remote_port=3121
When changing the default port used by a particular guest node or remote node, the
PCMK_remote_port variable must be set in that node’s
/etc/sysconfig/pacemaker file, and the cluster resource creating the guest node or remote node connection must also be configured with the same port number (using the
remote-port metadata option for guest nodes, or the
port option for remote nodes).
29.5. Upgrading systems with pacemaker_remote nodes
pacemaker_remote service is stopped on an active Pacemaker Remote node, the cluster will gracefully migrate resources off the node before stopping the node. This allows you to perform software upgrades and other routine maintenance procedures without removing the node from the cluster. Once
pacemaker_remote is shut down, however, the cluster will immediately try to reconnect. If
pacemaker_remote is not restarted within the resource’s monitor timeout, the cluster will consider the monitor operation as failed.
If you wish to avoid monitor failures when the
pacemaker_remote service is stopped on an active Pacemaker Remote node, you can use the following procedure to take the node out of the cluster before performing any system administration that might stop
Stop the node’s connection resource with the
pcs resource disable resourcenamecommand, which will move all services off the node. The connection resource would be the
ocf:pacemaker:remoteresource for a remote node or, commonly, the
ocf:heartbeat:VirtualDomainresource for a guest node. For guest nodes, this command will also stop the VM, so the VM must be started outside the cluster (for example, using
virsh) to perform any maintenance.
pcs resource disable resourcename
- Perform the required maintenance.
When ready to return the node to the cluster, re-enable the resource with the
pcs resource enablecommand.
pcs resource enable resourcename