Chapter 6 Linux Virtual Server Overview; A Basic Lvs Configuration - Red Hat ENTERPRISE LINUX AS 2.1 Installation Manual

Section 6.1:A Basic LVS Configuration
6 Linux Virtual Server Overview
As mentioned in the introduction, Red Hat Enterprise Linux AS LVS clustering uses a Linux machine
called the active router to send requests from the Internet to a pool of servers. To accomplish this, LVS
clusters consist of two basic machine classifications — the LVS routers (one active and one backup)
and a pool of real servers which provide the critical services.
The active router serves two roles in the cluster:
• To balance the load on the real servers.
• To check the integrity of the services on each of the real servers.
The backup router's job is to monitor the active router and assume its role in the event of failure.
To explain how LVS clusters perform these functions, let us look at a basic configuration.

6.1 A Basic LVS Configuration

Figure 6–1, A Basic LVS Configuration shows a simple LVS cluster consisting of two layers. On
the first layer are two LVS routers — one active and one backup. Each of the LVS routers have two
network interfaces per machine, one interface on the Internet and one on the private network, enabling
them to regulate traffic between the two networks. For this example the active router is using Network
Address Translation or NAT to direct traffic from the Internet to a variable number of real servers
on the second layer, which in turn provide the necessary services. Therefore, the real servers in this
example are connected to a dedicated private network segment and pass all public traffic back and
forth through the active LVS router. To the outside world, the server farm appears as one entity.
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