Novell SUSE LINUX ENTERPRISE SERVER 10 SP2 HEARTBEAT Manual page 19

Policy Engine (PE) and Transition Engine (TE)
Whenever the Designated Coordinator needs to make a cluster-wide change (react
to a new CIB), the Policy Engine is used to calculate the next state of the cluster
and the list of (resource) actions required to achieve it. The commands computed
by the Policy Engine are then executed by the Transition Engine. The DC will send
out messages to the relevant Cluster Resource Managers in the cluster, who then
use their Local Resource Managers (see
below) to perform the necessary resource manipulations. The PE/TE pair only runs
on the DC node.
Local Resource Manager (LRM)
The Local Resource Manager calls the local Resource Agents (see
Layer" (page 11) below) on behalf of the CRM. It can thus perform start / stop /
monitor operations and report the result to the CRM. The LRM is the authoritative
source for all resource related information on its local node.
Resource Layer
The fourth and highest layer is the Resource Layer. The Resource Layer includes one
or more Resource Agents (RA). A Resource Agent is a program, usually a shell script,
that has been written to start, stop, and monitor a certain kind of service (a resource).
The most common Resource Agents are LSB init scripts. However, Heartbeat also
supports the more flexible and powerful Open Clustering Framework Resource Agent
API. The agents supplied with Heartbeat are written to OCF specifications. Resource
Agents are called only by the Local Resource Manager. Third parties can include their
own agents in a defined location in the file system and thus provide out-of-the-box
cluster integration for their own software.
1.5.2 Process Flow
Many actions performed in the cluster will cause a cluster-wide change. These actions
can include things like adding or removing a cluster resource or changing resource
constraints. It is important to understand what happens in the cluster when you perform
such an action.
For example, suppose you want to add a cluster IP address resource. To do this, you
use either the cibadmin command line tool or the Heartbeat GUI tool to modify the
master CIB. It is not required to use the cibadmin command or the GUI tool on the
Local Resource Manager (LRM) (page 11)
Section "Resource
Overview 11