HP-UX OSRA for Web Services 2.5 Blueprint and Configuration Guide

the name cache, but flushing the cache more frequently puts a larger load on the DNS name
server as more requests are forwarded to it.
Load Balancing With Apache mod_jk
The Apache mod_jk module is a plug-in that handles communication between Tomcat and the
HP-UX Apache-based Web server. Load balancing with mod_jk eliminates many of the limitations
of DNS Round-Robin load balancing and does not require any additional hardware.
Figure 3-3 illustrates load balancing with mod_jk. The mod_jk module load balances between
several application servers. In most cases, the web server handles the static data and distributes
dynamic content to the application servers.
Figure 3-3 Load Balancing With mod_jk
When configuring mod_jk load balancing, you can do the following:
• Ensure that requests are not routed to a server that is not responding.
• Set up round-robin, or weighted round-robin to route requests to a server.
• Route all requests from the same session to the same server (sticky session).
DNS Load Balancing Configuration Example
This section describes how to configure DNS Round Robin load balancing and provides examples
of the files you must create and modify when setting up this configuration.
This example uses the hosts_to_named utility to convert the /etc/hosts file into the
appropriate Internet domain name server (named) configuration files. The goal is to configure
a virtual host name with multiple addresses, so that each time a client makes a request to the
host name, the client receives a different address, in round-robin order.
To configure DNS Round-Robinload balancing, follow these steps:
1. Configure named with the virtual server host name.
2. Tune the DNS cache.
For more information, see named(1m), named.conf(4), and the HP-UX IP Address and Client
Management Administrator's Guide.
Horizontal Scaling of Web and Application Servers 29