7
Configuration Considerations for Web Sites with Multiple Application Web Servers

This chapter describes additional configuration options available for deployments with two or more application Web servers.

This chapter contains these topics:

• Configuring Load Balancing and Failover

• Binding a Session to an Application Web Server

Configuring Load Balancing and Failover

For those requests that Oracle Web Cache cannot serve, you can distribute the requests over a set of application Web servers with Oracle Web Cache's load balancing feature. To configure load balancing, you prescribe the relative load of each application Web server.

See Also: "Load Balancing of Application Web Servers" for an overview of load balancing

1. Start Oracle Web Cache Manager.

   See Also: "Starting Oracle Web Cache Manager"

2. Configure application Web server settings in the Edit/Create Application Web Server dialog box, following the steps in "Task 3: Specify Web Site Settings". In Step 2 of the procedure, enter the number of concurrent connections that the application Web server can sustain in the Capacity field. The weighted load percentage of each application Web server is derived from the entered capacity.

When load balancing is configured and an application Web server is no longer available, Oracle Web Cache automatically performs backend failover of the application Web servers. Oracle Web Cache knows if an application Web server is down when a failover threshold has been met.

An application Web server can become unavailable if it is taken down for reconfiguration or there is a network or hardware failure. In these scenarios, Oracle Web Cache automatically distributes the load over the remaining application Web servers and polls the failed application Web server for its current up/down status until it is back online. Existing requests to the failed application Web server result in errors. However, new requests are directed to the other application Web servers. When the failed server returns to operation, Oracle Web Cache includes it in the load distribution.

See Also: "Task 3: Specify Web Site Settings" to configure the failover threshold

Binding a Session to an Application Web Server

See Also: "Application Web Server Binding" for an overview of application Web server binding

You can configure Oracle Web Cache to support application Web server session binding, whereby a user session is bound to an application Web server in order to maintain state for a period of time. To utilize this feature, the application Web server itself must maintain state, that is, it must be stateful.

As long as the session information is contained within a session cookie or an embedded URL parameter, Oracle Web Cache can keep track of sessions between Web browsers and application Web servers. This enables Oracle Web Cache to bind a particular user session to a specific application Web server.

To configure Oracle Web Cache to support binding a user session to application Web servers that are stateful:

1. Start Oracle Web Cache Manager.

   See Also: "Starting Oracle Web Cache Manager"

2. In the navigator pane, select Administering Web Sites > Session Management > Session Binding.

   The Application Web Server Session Binding page appears in the right pane.

3. In the Application Web Server Session Binding page, choose Edit.

   The Change Application Web Server Session Binding dialog box appears.

4. From the Please select a session list, select a session and skip to Step 7.

   If the sessions listed do not contain the definition you require, choose Create A New Session Definition to create a new session definition. The Edit/Create Session Definitions dialog box appears. Continue to Step 5.

5. Create a session definition in the Edit/Create Session Definitions dialog box:
   1. In the Session Name field, enter an easy-to-remember unique name for the attribute.

   2. Enter the cookie name in the Cookie Name field and/or the embedded URL parameter in the URL Parameter field.

      If you enter both a cookie name and an embedded URL parameter, keep in mind that both must be used to support the same session. If they support different sessions, create separate session definitions. You can specify up to 20 session definitions for each page.

      Note: Oracle Web Cache requires a session cookie to perform session binding. If browsers do not support cookies and you want to use an embedded URL parameter for the session, then perform the following in order for Oracle Web Cache to perform session binding on the session: In addition to the URL Parameter field, specify a cookie name for the session in the Cookie Name field. Ensure that your application Web server returns a Set-Cookie response-header with the value of the session every time a session is created. Set-Cookie: cookie=value Set value to the same value as set in the URL Parameter field. Oracle Web Cache uses the Set-Cookie response header, even if ignored by browsers, to locate the session cookie value for session binding. See Also: http://rfc.net/rfc2965.html for further information about the Set-Cookie response header

Note: When a session cookie expires, Oracle Web Cache does not continue to bind the user session to the application Web server. Instead, Oracle Web Cache uses load balancing to choose an application Web server. To avoid pages being served past the browser session expiration time, ensure that the session cookie expires before the application Web server expires the browser session.

3. Choose Submit.

6. In the Change Application Web Server Session Binding dialog box, select the session definition from the Please select a session list.

7. In the Inactivity Timeout field, enter the number of minutes you want Oracle Web Cache to wait before timing out an inactive session to the application Web server. Oracle Corporation recommends setting the value to a higher value than the inactivity timeout set for the Web site.

8. Choose Submit.

9. Apply changes and restart Oracle Web Cache:
   1. In the Oracle Web Cache main window, choose Apply Changes.

   2. In the navigator pane, select Administering Oracle Web Cache > Web Cache Operations.

      The Oracle Web Cache Operations page appears in the right pane.

   3. In the Oracle Web Cache Operations page, choose Stop and then Start to restart Oracle Web Cache.