Chapter 7. Using load balancing 189
and system-level load balancing. In application-level load balancing, the instances are
identified by IP, port, and protocol. In system-level load balancing, the instances are identified
solely by IP address. Once the managed servers are configured to run in this environment,
system-level performance data is sent to the domain manager by each of the managed
servers in the management domain. If the managed server system is running
ARM-instrumented applications, additional performance data can be sent regarding the
performance of the applications themselves.
The load balancer registers those instances (system or application) as a group that it wishes
to load balance to and associates them to the domain manager. The load balancer can then
start obtaining EWLM distribution recommendations for each instance within the group. More
than one group may be registered at any one time. Using the EWLM recommended
distribution, the load balancer can forward incoming requests in a manner that provides better
end-to-end business response time. At this time, the load balancers provided by Cisco
Systems Inc. and Nortel Networks both support system-level balancing. Application-level
balancing is only performed by Cisco Systems Inc. load balancers.
In the next section we discuss installation and configuration.
7.2.1 Managed server
Currently, the managed servers running on the following operating systems have load
balancing support:
– IBM AIX 5.2 ML03
– Microsoft Windows 2000 server (32-bit)
– Microsoft Windows 2003 server (32-bit)
– Sun Microsystems Solaris 8 (SPARC Platform Edition)
– Sun Microsystems Solaris 9 (SPARC Platform Edition)
With this level of support, the EWLM domain manager together with the load balancer can
perform system-level load balancing from the information provided by the managed server. If
the applications running on these operating systems are ARM-enabled, then application-level
load balancing can occur as well.
Installation and configuration
Installation and configuration are specific to each operating system.
AIX
AIX 5.2 ML03 has the platform support installed. There is a special fileset on the EWLM CD
that must be installed. See “Configuring managed servers on AIX and Windows” on page 46.
Windows and Solaris
The Virtualization Engine Install Shield installs the system-specific code and the EWLM
common code. The installation of the system-specific package makes all changes to the
operating system required for it to run. For Solaris, refer to “Managed server on Solaris” on
page 54.
Solaris only
Additionally, in order for applications running on a Solaris operating system to participate in
load balancing with EWLM, they need to have a linkage to the shared library object
/usr/lib/libnetwlm_applib.so. One method to accomplish the link is via a shell script.
Example 7-1 shows an application called Webserv which has set the environment variable
LD_PRELOAD to point to the libnetwlm_applib.so library. Using this shell script method
allows the libnetwlm_applib.so library to be used only on those applications which the
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