Configuring simple load balancing across multiple application server profiles

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:
1. Expand Servers > Server Types and click WebSphere application servers > server_name.
2. Under Container Settings, expand Web Container Settings, and click Web container.
3. Under Additional Properties, click Custom properties > New.
4. In the Name field, enter HttpSessionCloneId.
5. In the Value field, enter a unique value for the server. The unique value must be 8 - 9 alphanumeric characters; for example, test1234
6. Click Apply or OK.
7. Click Save to save the configuration changes to the master configuration.
Optional: Configure session persistence, if needed.
If you require session failover capability, you must configure session persistence. Persistence of the session object to a database is the only option for session failover with WebSphere Application Server. To configure session persistence by 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 pluginCfgMergetool 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.
To use the pluginCfgMerge tool, complete the following steps:
1. Rename the plugin-cfg.xml files to a unique name across your application server profiles.
2. Copy the plugin-cfg.xml file for all stand-alone application server profiles into a common directory.
3. Override any existing differences in global properties by modifying one of your xml files to those values you require in your new xml file. This modified file is used by the pluginCfgMerge tool as the source of global properties for the new xml file.
4. Use the pluginCfgMerge tool to combine the plugin-cfg.xml files from each of the application server profiles into a single output file. Use the xml file that is modified in the previous step as the first file in the pluginCfgMerge command string. Define the name of the outputted file by defining the resulting_plugin_configuration_file variable value in the command string. The resulting_plugin_configuration_file variable value must match the name that is defined within the respective web server definition of the admin console, which by default is plugin-cfg.xml. Your command resembles one of the following examples:
```
install_root/bin/pluginCfgMerge.sh plugin_configuration_file1 plugin_configuration_file2 resulting_plugin_configuration_file
```
```
install_root\bin\pluginCfgMerge.bat plugin_configuration_file1 plugin_configuration_file2 resulting_plugin_configuration_file
```
Copy the merged plugin-cfg.xml 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.