1.2. High Availability Add-On Introduction

The High Availability Add-On is an integrated set of software components that can be deployed in a variety of configurations to suit your needs for performance, high-availability, load balancing, scalability, file sharing, and economy.

The High Availability Add-On consists of the following major components:

Cluster infrastructure — Provides fundamental functions for nodes to work together as a cluster: configuration-file management, membership management, lock management, and fencing.
High-availability Service Management — Provides failover of services from one cluster node to another in case a node becomes inoperative.
Cluster administration tools — Configuration and management tools for setting up, configuring, and managing a the High Availability Add-On. The tools are for use with the Cluster Infrastructure components, the High-availability and Service Management components, and storage.

You can supplement the High Availability Add-On with the following components:

Red Hat GFS2 (Global File System 2) — Part of the Resilient Storage Add-On, this provides a cluster file system for use with the High Availability Add-On. GFS2 allows multiple nodes to share storage at a block level as if the storage were connected locally to each cluster node.
Cluster Logical Volume Manager (CLVM) — Part of the Resilient Storage Add-On, this provides volume management of cluster storage.
Load Balancer Add-On — Routing software that provides IP-Load-balancing. the Load Balancer Add-On runs in a pair of redundant virtual servers that distributes client requests evenly to real servers that are behind the virtual servers.