Simple load balancing distributes HTTP requests across multiple IBM®
WebSphere® Application Server instances. You can configure simple load
balancing to provide failover of an application state that is maintained in an HTTP
session.
Before you begin
Supported configurations: This offering applies to stand-alone
application server profiles for IBM
WebSphere Application Server. This offering does not include a centralized
management capability such as the deployment manager in WebSphere Application Server Network Deployment.
About this task
You can configure simple load balancing capability with
WebSphere Application Server by combining the plug-in configuration files of
multiple stand-alone application server profiles into a single configuration file.
The number of
configuration files that you can combine are bound by the limits that exist in the WebSphere Application Server license agreement. You can use the following
different configurations of the application server to combine the plug-in configuration files of
multiple application server profiles into a single output file:
- Using multiple stand-alone base application server profiles
- Using multiple stand-alone base application server profiles with an administrative agent. For
more information, see the documentation on configuring simple load balancing across multiple
stand-alone base application server profiles with an administrative agent.
- Using multiple stand-alone base application server profiles with an administrative agent that
uses the job manager. The job manager function is a part of WebSphere Application Server Network Deployment. However, you can use the job manager function
with stand-alone, base application server profiles. For more information, see the documentation on
configuring simple load balancing across multiple stand-alone, base application server profiles with
an administrative agent that uses the job manager.
Complete the following steps to configure simple load balancing across multiple stand-alone,
base application server profiles:
Procedure
-
Install WebSphere Application Server and create application server
profiles.
For more information, see the documentation on WebSphere Application Server installation and application server profiles.
-
Install the enterprise application or web module.
For more information, see the documentation on the methods for installing applications or
modules.
-
Determine whether you require session affinity.
Session affinity directs requests from a client to a specific application server. The application
that is state maintained in the HTTP session is accessed in the HTTP session cache, which is local
to the application server. Session affinity provides higher performance than database persistence of
the session object, alone. Without session affinity, session requests must be obtained from the
database if they are sent to a server that does not have the session object in the local cache.
- Optional:
Configure a unique HTTP session clone ID for each application server.
If you require session affinity, you must complete this step.
You can configure a unique HTTP session clone ID by usingwsadmin scripting or
the administrative console. To use wsadmin commands for the Jython or Jacl
programming language, see the documentation on using scripting to configure a unique HTTP session
clone ID for each application server. To configure a unique HTTP session clone ID by using the
administrative console, complete the following steps:
-
Expand and click .
-
Under Container Settings, expand Web Container
Settings, and click Web container.
-
Under Additional Properties, click .
-
In the Name field, enter
HttpSessionCloneId.
-
In the Value field, enter a unique value for the server. The unique
value must be 8 - 9 alphanumeric characters; for example, test1234
-
Click Apply or OK.
-
Click Save to save the configuration changes to the master
configuration.
- Optional:
If you require session failover capability, configure session persistence.
If you require session failover capability, you must complete this step. Persistence of the
session object to a database is the only option for session failover with WebSphere Application Server. To configure session persistence using the
administrative console, see the documentation on configuring database session persistence. To
configure database session persistence by using wsadmin commands for the Jython or Jacl programming
language, see the documentation on using scripting to configure database session persistence.
-
Restart the server.
-
Generate the plugin-cfg.xml file for each application server by using the
GenPluginCfg script, the administrative console, or wsadmin
scripting.
See the topic GenPluginCfg command for a description of how to use the GenPluginCfg
script to generate the plugin-cfg.xml file.
See the topic Implementing a web server plug-in for a description of how to use the
administrative console to generate the plugin-cfg.xml file.
See the topic Regenerating the node plug-in configuration using scripting for a
description of how to use wsadmin scripting to generate the
plugin-cfg.xml file.
-
Merge the plugin-cfg.xml files from multiple application server
nodes.
You can either manually merge the plugin-cfg.xml files or use the
pluginCfgMerge tool to automatically merge the
plugin-cfg.xml files from multiple application server profiles into a single
output file. The pluginCfgMerge tool scripts
pluginCfgMerge.bat and pluginCfgMerge.sh are located in
the install_root/bin directory.
Before you begin the merge, review any differences between global variables that are defined in
the two
plugin.cfg.xmlfiles to be merged, for example the global variables
refreshInterval or
esiEnable. Determine which settings best
suit the environment to be governed by the merged
plugin.cfg.xml files. The
pluginCfgMerge tool uses the first file in the command string as the source of
global properties for the new xml file.
Note: You need to re-merge the files when you make any
changes to the WebSphere Application Server environment that require a new
plug-in generation.
-
Copy the merged output file to the
plugin_installation_root/config/web_server_name/ directory
on the web server host.
-
Ensure that the merged output files have the correct operating system file access permissions
for the merged output file.
These file access permissions allow the HTTP server plug-in process to read the file.
Results
When you complete this process, you have one plug-in configuration file for multiple
stand-alone application server profiles.