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. GFS2 cluster file system requires a cluster infrastructure.
  • Cluster Logical Volume Manager (CLVM) — Part of the Resilient Storage Add-On, this provides volume management of cluster storage. CLVM support also requires cluster infrastructure.
  • Load Balancer Add-On — Routing software that provides high availability load balancing and failover in layer 4 (TCP) and layer 7 (HTTP, HTTPS) services. The Load Balancer Add-On runs in a cluster of redundant virtual routers that uses load algorithms to distribute client requests to real servers, collectively acting as a virtual server. It is not necessary to use the Load Balancer Add-On in conjunction with Pacemaker.