Installation guide

Chapter 1. High Availability Add-On Overview
The High Availability Add-On is a clustered system that provides reliability, scalability, and
availability to critical production services. The following sections provide a high-level description of
the components and functions of the High Availability Add-On:
Section 1.1, “Cluster Basics”
Section 1.2, “ High Availability Add-On Introduction”
Section 1.3, “ Cluster Infrastructure”
1.1. Clust er Basics
A cluster is two or more computers (called nodes or members) that work together to perform a task.
There are four major types of clusters:
Storage
High availability
Load balancing
High performance
Storage clusters provide a consistent file system image across servers in a cluster, allowing the
servers to simultaneously read and write to a single shared file system. A storage cluster simplifies
storage administration by limiting the installation and patching of applications to one file system.
Also, with a cluster-wide file system, a storage cluster eliminates the need for redundant copies of
application data and simplifies backup and disaster recovery. The High Availability Add-On provides
storage clustering in conjunction with Red Hat GFS2 (part of the Resilient Storage Add-On).
High availability clusters provide highly available services by eliminating single points of failure and
by failing over services from one cluster node to another in case a node becomes inoperative.
Typically, services in a high availability cluster read and write data (via read-write mounted file
systems). Therefore, a high availability cluster must maintain data integrity as one cluster node takes
over control of a service from another cluster node. Node failures in a high availability cluster are not
visible from clients outside the cluster. (high availability clusters are sometimes referred to as failover
clusters.) The High Availability Add-On provides high availability clustering through its High
Availability Service Management component, rg manag er.
Load-balancing clusters dispatch network service requests to multiple cluster nodes to balance the
request load among the cluster nodes. Load balancing provides cost-effective scalability because
you can match the number of nodes according to load requirements. If a node in a load-balancing
cluster becomes inoperative, the load-balancing software detects the failure and redirects requests to
other cluster nodes. Node failures in a load-balancing cluster are not visible from clients outside the
cluster. Load balancing is available with the Load Balancer Add-On.
High-performance clusters use cluster nodes to perform concurrent calculations. A high-performance
cluster allows applications to work in parallel, therefore enhancing the performance of the
applications. (High performance clusters are also referred to as computational clusters or grid
computing.)
⁠Chapt er 1 . High Availabilit y Add- O n Overview
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