Red Hat ENTERPRISE LINUX 5 - VIRTUAL SERVER ADMINISTRATION Manual page 60

Appendix A. Using LVS with Red Hat Cluster
A three-tier configuration is required to provide dynamic content. While a two-tier LVS configuration is
suitable if the Web servers serve only static Web content (consisting of small amounts of infrequently
changing data), a two-tier configuration is not suitable if the Web servers serve dynamic content.
Dynamic content could include product inventory, purchase orders, or customer databases, which
must be consistent on all the Web servers to ensure that customers have access to up-to-date and
accurate information.
Each tier provides the following functions:
• First tier — LVS routers performing load-balancing to distribute Web requests.
• Second tier — A set of Web servers to serve the requests.
• Third tier — A Red Hat Cluster to serve data to the Web servers.
Figure A.1, "LVS with a Red Hat Cluster", client systems issue
In an LVS configuration like the one in
requests on the World Wide Web. For security reasons, these requests enter a Web site through
a firewall, which can be a Linux system serving in that capacity or a dedicated firewall device. For
redundancy, you can configure firewall devices in a failover configuration. Behind the firewall are LVS
load-balancing routers, which can be configured in an active-standby mode. The active load-balancing
router forwards the requests to the set of Web servers.
Each Web server can independently process an HTTP request from a client and send the response
back to the client. LVS enables you to expand a Web site's capacity by adding Web servers behind the
LVS routers; the LVS routers perform load balancing across a wider set of Web servers. In addition, if
a Web server fails, it can be removed; LVS continues to perform load balancing across a smaller set of
Web servers.
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