Installation guide

84 Chapter 6. Introduction to Linux Virtual Server

hardware to implement a fully redundant environment in which services can run uninter-

rupted by hardware failures.

However, fault tolerant systems do not account for operator and software errors which

Red Hat Enterprise Linux can address through service redundancy. Also, since Red Hat

Enterprise Linux is designed to run on commodity hardware, it creates an environment

with a high level of system availability at a fraction of the cost of fault tolerant hardware.

6.2. Basic Conﬁgurations

While Red Hat Enterprise Linux can be conﬁgured in a variety of different ways, the con-

ﬁgurations can be broken into two major categories:

• High-availability clusters using Red Hat Cluster Manager

• Load-balancing clusters using Linux Virtual Servers

This part explains what a load-balancing cluster system is and how to conﬁgure a load-

balancing system using Linux Virtual Servers on Red Hat Enterprise Linux.

6.2.1. Load-Balancing Clusters Using Linux Virtual Servers

To an outside user accessing a hosted service (such as a website or database application),

a Linux Virtual Server (LVS) cluster appears as one server. In reality, however, the user is

actually accessing a cluster of two or more servers behind a pair of redundant LVS routers

that distribute client requests evenly throughout the cluster system. Load-balanced clus-

tered services allow administrators to use commodity hardware and Red Hat Enterprise

Linux to create continuous and consistent access to all hosted services while also address-

ing availability requirements.

An LVS cluster consists of at least two layers. The ﬁrst layer is composed of a pair of

similarly conﬁgured Linux machines or cluster members. One of these machine acts as the

LVS routers, conﬁgured to direct requests from the Internet to the cluster. The second layer

consists of a cluster of machines called real servers. The real servers provide the critical

services to the end-user while the LVS router balances the load on these servers.

For a detailed overview of LVS clustering, refer to

Chapter 7 Linux Virtual Server Overview.