Novell LINUX ENTERPRISE 11 - HIGH AVAILABILITY, Manual, Page: 23 / 298

taining a list of (resource) actions and dependencies to achieve the next cluster
state. The PE runs on every node to speed up DC failover.
Local Resource Manager (LRM)
The LRM calls the local Resource Agents (see Section “Resource Layer” (page 13))
on behalf of the CRM. It can thus perform start / stop / monitor operations and report
the result to the CRM. It also hides the difference between the supported script
standards for Resource Agents (OCF, LSB, Heartbeat Version 1). The LRM is the
authoritative source for all resource-related information on its local node.
Resource Layer
The highest layer is the Resource Layer. The Resource Layer includes one or more
Resource Agents (RA). Resource Agents are programs (usually shell scripts) that have
been written to start, stop, and monitor a certain kind of service (a resource). Resource
Agents are called only by the LRM. 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.
1.4.2 Process Flow
SUSE Linux Enterprise High Availability Extension uses Pacemaker as CRM. The
CRM is implemented as daemon (
crmd
) that has an instance on each cluster node.
Pacemaker centralizes all cluster decision-making by electing one of the crmd instances
to act as a master. Should the elected crmd process (or the node it is on) fail, a new one
is established.
A CIB, reflecting the cluster’s configuration and current state of all resources in the
cluster is kept on each node. The contents of the CIB are automatically kept in sync
across the entire cluster.
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
can use one of the command line tools or the GUI to modify the CIB. It is not required
to perform the actions on the DC, you can use either tool on any node in the cluster and
Conceptual Overview 13