Two-Tier Lvs Topology - Red Hat Enterprise Linux 5 Cluster Suite Overview

Chapter 1. Red Hat Cluster Suite Overview
• Synchronize the data across the real servers.
• Add a third layer to the topology for shared data access.
The first option is preferred for servers that do not allow large numbers of users to upload or change
data on the real servers. If the real servers allow large numbers of users to modify data, such as an e-
commerce website, adding a third layer is preferable.
There are many ways to synchronize data among real servers. For example, you can use shell scripts
to post updated web pages to the real servers simultaneously. Also, you can use programs such as
rsync to replicate changed data across all nodes at a set interval. However, in environments where
users frequently upload files or issue database transactions, using scripts or the rsync command
for data synchronization does not function optimally. Therefore, for real servers with a high amount of
uploads, database transactions, or similar traffic, a three-tiered topology is more appropriate for data
synchronization.

1.8.1. Two-Tier LVS Topology

Figure 1.17, "Two-Tier LVS Topology"
shows a simple LVS configuration consisting of two tiers:
LVS routers and real servers. The LVS-router tier consists of one active LVS router and one backup
LVS router. The real-server tier consists of real servers connected to the private network. Each LVS
router has two network interfaces: one connected to a public network (Internet) and one connected
to a private network. A network interface connected to each network allows the LVS routers to
regulate traffic between clients on the public network and the real servers on the private network. In
Figure 1.17, "Two-Tier LVS Topology", the active LVS router uses Network Address Translation (NAT)
to direct traffic from the public network to real servers on the private network, which in turn provide
services as requested. The real servers pass all public traffic through the active LVS router. From the
perspective of clients on the public network, the LVS router appears as one entity.
Figure 1.17. Two-Tier LVS Topology
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