Installation guide

180 Appendix B:Supplementary Software Information
Figure B–1 Cluster in an LVS Environment
In a Piranha configuration, client systems issue 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 capac-
ity or a dedicated firewall device. For redundancy, you can configure firewall devices in a failover
configuration. Behind the firewall are Piranha load-balancing systems, which can be configured in an
active-standby mode. The active load-balancing system forwards the requests to a set of Web servers.
Each Web server can independently process an HTTP request from a client and send the response back
to the client. Piranha enables an administrator to expand a Web site’s capacity by adding Web servers
to the load-balancing systems’ set of active Web servers. In addition, if a Web server fails, it can be
removed from the set.
This Piranha configuration is particularly suitable if the Web servers serve only static Web content,
which consists of small amounts of infrequently changing data, such as corporate logos, that can be
easily duplicated on the Web servers. However, this configuration is not suitable if the Web servers
serve dynamic content, which consists of information that changes frequently. Dynamic content could
include a product inventory, purchase orders, or customer database, which must be consistent on all
the Web servers to ensure that customers have access to up-to-date and accurate information.
To serve dynamic Web content in a Piranha configuration, add a cluster behind the Web servers, as
shown in the previous figure. This combination of Piranha and Red Hat Cluster Manager allows
for the configuration of a high-integrity, no-single-point-of-failure e-commerce site. The cluster can
run a highly-available instance of a database or a set of databases that are network-accessible to the
Web servers.