Chapter 11: The Linux Virtual Server: Introduction and Theory

Overview

This chapter will introduce the cluster load-balancing software called IP Virtual Server (IPVS). The IPVS software is a collection of kernel patches that were merged into the stock version of the Linux kernel starting with version 2.4.23. When combined with the kernel's routing and packet-filtering capabilities (discussed in Chapter 2) the IPVS-enabled kernel lets you turn any computer running Linux into a cluster load balancer. Together, the IPVS-enabled cluster load balancer and the cluster nodes are called a Linux Virtual Server (LVS).

The LVS cluster load balancer accepts all incoming client computer requests for services and decides which cluster node should reply to each request. The load balancer is sometimes called an LVS Director or simply a Director. In this book the terms LVS Director, Director, and load balancer all refer to the same thing.

The nodes inside an LVS cluster are called real servers, and the computers that connect to the cluster to request its services are called client computers. The client computers, the Director, and the real servers communicate with each other using IP addresses the same way computers have always exchanged packets over a network; however, to make it easier to discuss this network communication, the LVS community has developed a naming convention to describe each type of IP address based on its role in the network conversation. So before we consider the different types of LVS clusters and the choices you have for distributing your workload across the cluster nodes (called scheduling methods), let's look at this naming convention and see how it helps describe the LVS cluster.