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

Figure 3-1 Hardware Load Balancing
Typically the hardware load balancer is configured with a virtual IP address. When a web client
requests a web service, the load balancer translates the virtual IP address into the address of one
of the application servers. The request is passed to an application server based on the translated
address and based on an allocation policy. The allocation policy can define the minimum response
time required by the server, the number of requests allowed to a server, the server weight, and
so on. The load balancer typically does not route requests to an unavailable application server.
In practice, you can have many servers, each serving the same web session, or one server, in the
cluster, serving a complete web session.
When configuring any load balancer, consider the storage of session information. If multiple
servers serve a session, they must have access to the same session information. This information
must be stored, updated, and made available to each of the servers serving the session. When a
single application server serves a web session, the session information can be stored on the server
serving the web session.
DNS Round-Robin Load Balancing
DNS round-robin load balancing provides load balancing without requiring additional hardware.
With DNS round-robin load balancing, you assign the IP address of several application servers
to a virtual server name, such as www.myservice.com. When a web client requests a web resource
from the virtual server name, DNS assigns one of the IP addresses through the DNS named
server. Subsequent requests to DNS to resolve the virtual server name are assigned to the next
IP address that is in line until all the available addresses have been assigned. The IP assigned
application servers become equally loaded because incoming web service requests are evenly
distributed among them.
Figure 3-2 (page 28) shows an example of a DNS load balancing configuration.
Horizontal Scaling of Web and Application Servers 27