Red Hat Cluster Manager Overview - Red Hat CLUSTER SUITE - CONFIGURING AND MANAGING A CLUSTER 2006 Manual

Red Hat Cluster Manager Overview

Red Hat Cluster Manager allows administrators to connect separate systems (called mem-
bers or nodes) together to create failover clusters that ensure application availability and
data integrity under several failure conditions. Administrators can use Red Hat Cluster
Manager with database applications, file sharing services, web servers, and more.
To set up a failover cluster, you must connect the nodes to the cluster hardware, and con-
figure the nodes into the cluster environment. The foundation of a cluster is an advanced
host membership algorithm. This algorithm ensures that the cluster maintains complete
data integrity by using the following methods of inter-node communication:
Network connections between the cluster systems
•
A Cluster Configuration System daemon (ccsd) that synchronizes configuration between
•
cluster nodes
To make an application and data highly available in a cluster, you must configure a cluster
service, an application that would benefit from Red Hat Cluster Manager to ensure high
availability. A cluster service is made up of cluster resources, components that can be failed
over from one node to another, such as an IP address, an application initialization script,
or a Red Hat GFS shared partition. Building a cluster using Red Hat Cluster Manager
allows transparent client access to cluster services. For example, you can provide clients
with access to highly-available database applications by building a cluster service using
Red Hat Cluster Manager to manage service availability and shared Red Hat GFS storage
partitions for the database data and end-user applications.
You can associate a cluster service with a failover domain, a subset of cluster nodes that
are eligible to run a particular cluster service. In general, any eligible, properly-configured
node can run the cluster service. However, each cluster service can run on only one cluster
node at a time in order to maintain data integrity. You can specify whether or not the nodes
in a failover domain are ordered by preference. You can also specify whether or not a
cluster service is restricted to run only on nodes of its associated failover domain. (When
associated with an unrestricted failover domain, a cluster service can be started on any
cluster node in the event no member of the failover domain is available.)
You can set up an active-active configuration in which the members run different cluster
services simultaneously, or a hot-standby configuration in which primary members run all
the cluster services, and a backup member takes over only if a primary member fails.
If a hardware or software failure occurs, the cluster automatically restarts the failed node's
cluster services on the functional node. This cluster-service failover capability ensures that
no data is lost, and there is little disruption to users. When the failed node recovers, the
cluster can re-balance the cluster services across the nodes.
Chapter 1.