Introduction

Thank you for purchasing Red Hat High Availability Server 1.0. With this product, it is possible to create solutions that can withstand many common hardware and software failures, and still provide service to your customers. In addition, because Red Hat High Availability Server allows more than one computer to work together to service your customers' needs, maintenance and upgrades can be planned and executed without an interruption in service.

This manual will guide you through the following steps in deploying a solution based on Red Hat High Availability Server:

• Begin to learn more about the underlying technology in this introduction, so that you can start to think about the configuration that would best fit your needs.

• Learn how to install Red Hat Linux 6.2 (the operating system on which Red Hat High Availability Server is based).

• Learn about the Failover Services (FOS) technology. FOS is used to create pairs of Linux-based systems that provide the services used by your customers, as well as implementing a backup system that automatically takes control at the first sign of problems.

• Learn about the Linux Virtual Server (LVS) technology. Like FOS, LVS can be used to create pairs of Linux-based systems that act as each other's backup. However, LVS goes a step further. Instead of the two Linux-based systems actually providing your services, they instead monitor and load-balance a pool of systems (that may or may not be Linux-based), making possible a wider array of performance and capacity options.

• Learn about the Piranha Web Interface, which uses an intuitive graphical interface to configure your Piranha system.

Let's start by taking a quick look at the technology behind Red Hat High Availability Server.

Technology Overview

Red Hat High Availability Server uses Piranha to implement highly-available solutions. Piranha is a collection of programs that interact with each other to provide a clustering solution. It is vital to note that cluster computing consists of two distinct branches:

• Compute clustering (such as beowulf) uses multiple machines to provide greater computing power for computationally-intensive tasks. This type of clustering is not addressed by Piranha.

• High Availability (or HA) clustering uses various technologies to gain an extra level of reliability for a service. HA clustering is the focal point for Piranha.

Please Note

The clustering technology described in this document should not be confused with fault tolerance. Fault tolerant systems use highly-specialized (and expensive) hardware to implement a fully-redundant environment in which services can run, uninterrupted by the most common failure modes. Red Hat High Availability Server is designed to run on readily-available hardware and to take proactive measures when a system fault is detected. This results in an environment that approaches (but does not reach) the availability of fault tolerant systems, but at a fraction of the cost.

Let's take a look at some sample configurations, using both FOS and LVS as the base technology. Note that the boxes in the following diagrams (and the terms used to describe them) designate roles rather than specific systems. Also keep in mind that, due to the variety of ways in which the underlying technologies may be deployed, you will find that various terms may be used interchangably throughout this and other cluster-related documents. Although a cluster may be configured such that each role is carried out by a dedicated system, there is no technological requirement for this. However, capacity planning or system administration-related issues may dictate that dedicated systems be used for the various roles in a given cluster.

	Please Note
	Due to the variety of ways in which the underlying technologies may be deployed, you will find that various terms may be used interchangably throughout this and other documents. While every attempt has been made to define each term as it is first used,