Installation guide

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. T wo-T ier LVS T opology

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.

Red Hat Ent erprise Linux 5 Clust er Suit e Overview