Red Hat CLUSTER SUITE - CONFIGURING AND MANAGING A CLUSTER 2006 Manual page 20

4
maintain application availability and data integrity. For example, if a node completely
fails, a healthy node (in the associated failover domain, if used) starts the service
or services that the failed node was running prior to failure. Cluster services already
running on the healthy node are not significantly disrupted during the failover process.
Note
For Red Hat Cluster Suite 4, node health is monitored through a cluster network
heartbeat. In previous versions of Red Hat Cluster Suite, node health was monitored
on shared disk. Shared disk is not required for node-health monitoring in Red Hat
Cluster Suite 4.
When a failed node reboots, it can rejoin the cluster and resume running the cluster
service. Depending on how the cluster services are configured, the cluster can re-
balance services among the nodes.
Manual cluster-service relocation capability
In addition to automatic cluster-service failover, a cluster allows you to cleanly stop
cluster services on one node and restart them on another node. You can perform
planned maintenance on a node system while continuing to provide application and
data availability.
Event logging facility
To ensure that problems are detected and resolved before they affect cluster-service
availability, the cluster daemons log messages by using the conventional Linux syslog
subsystem.
Application monitoring
The infrastructure in a cluster monitors the state and health of an application. In this
manner, should an application-specific failure occur, the cluster automatically restarts
the application. In response to the application failure, the application attempts to be
restarted on the node it was initially running on; failing that, it restarts on another
cluster node. You can specify which nodes are eligible to run a cluster service by
assigning a failover domain to the cluster service.
1.1.1. Red Hat Cluster Manager Subsystem Overview
Table 1-1 summarizes the GFS Software subsystems and their components.
Chapter 1. Red Hat Cluster Manager Overview