Using ClusterCATS
Configuring Clusters

Session-aware load balancing

Managing a web application's state in a clustered environment can be challenging. By default, web application, session, and server variables that are stored in memory or a repository during a user session do not persist during a server redirection. Consequently, the web server cannot maintain the application's state correctly.

To overcome this problem, ClusterCATS provides a session-aware load-balancing feature that lets you maintain application state in a clustered environment.

One way to maintain your web application's state is to create session variables that are stored on the web server. For an e-commerce website that is clustered, it is vital that users do not get redirected to another server in the middle of their session. If they did, their online transactions would be interrupted, making for an unsuccessful and frustrating user experience.

To ensure that users are not redirected from the server on which they start their session, ClusterCATS provides a built-in feature for enabling session-aware load balancing. Sometimes referred to as a "sticky" server, session-aware load balancing guarantees that users will not get bumped from the server on which they start their session until the session is complete, regardless of the load thresholds that have been defined for that server.

Note:   Session-aware load balancing may not work if you use absolute hyperlinks in your web pages. Absolute links route the HTTP request back to the cluster entry point and redirect according to the current load threshold without regard to the state of the requesting client. To avoid inadvertent loss of state, use only relative linking in your web pages.

This section describes the following:

• "Enabling session-aware load balancing on Windows"
• "Enabling session-aware load balancing on UNIX"

Enabling session-aware load balancing on Windows

To enable session-aware load balancing:

1. Open the ClusterCATS Explorer and select a cluster.
2. Select Configure > Administration or right-click the cluster and select Configure > Administration.

   The cluster Properties dialog box appears.

3. Select the Session State Management check box.
4. Click OK.

Enabling session-aware load balancing on UNIX

To enable session-aware load balancing:

1. In ClusterCATS Web Explorer, click the Show Cluster link.
2. Enter the fully qualified host name of a server for which you want to configure session-aware load balancing in the Web Server Name field.
3. Click OK.

   The Cluster Member List page appears:

   

4. Click the Administration link under Cluster Attributes.

   The Cluster Administration page appears:

   

5. Select the Enable session-aware load balancing check box.
6. Click OK to enable session-aware load balancing for the selected cluster.

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