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Chapter 1.
Linux Virtual Server Overview
Linux Virtual Server (LVS) is a set of integrated software components for balancing the IP load
across a set of real servers. LVS runs on a pair of equally configured computers: one that is an
active LVS router and one that is a backup LVS router. The active LVS router serves two roles:
• To balance the load across the real servers.
• To check the integrity of the services on each real server.
The backup LVS router monitors the active LVS router and takes over from it in case the active
LVS router fails.
This chapter provides an overview of LVS components and functions, and consists of the
following sections:
•
Section 1, "A Basic LVS Configuration"
•
Section 2, "A Three-Tier LVS Configuration"
•
Section 3, "LVS Scheduling Overview"
•
Section 4, "Routing Methods"
•
Section 5, "Persistence and Firewall Marks"
•
Section 6, "LVS — A Block Diagram"
1. A Basic LVS Configuration
Figure 1.1, "A Basic LVS Configuration"
layers. On the first layer are two LVS routers — one active and one backup. Each of the LVS
routers has two network interfaces, 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 servers appears as one entity.
shows a simple LVS configuration consisting of two
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