The pacemaker program is the Cluster Resource Manager in Unix operation system cluster. It decides which resoure starts on what node in respect to the availability of nodes and the configuration constraints. Please see the pacemaker page for the description of the cluster software.
When you operate a cluster you want to know, what it's status is or get alerts if something happens. In short, enjoy all the benefits of a Network Monitoring System (NMS). The internet standard protocol for NMS to monitor devices and applications is the Simple Network Management Protocol (SNMP).
In this article I will describe, how you can set up a SNMP agent that publishes the state of your cluster nodes and resources. Every NMS (OpenNMS, Zabbix, nagios or the commercial alternatives) will be able to monitor the cluster properly.