Red Hat Cluster Manager Overview

Red Hat Cluster Manager allows administrators to connect separate systems (called members 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 configure 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 nodes run all the cluster services, and a backup cluster system takes over only if the primary nodes fail.

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.

In addition, you can cleanly stop the cluster services running on a cluster system and then restart them on another system. This cluster-service relocation capability allows you to maintain application and data availability when a cluster node requires maintenance.