ZK Configuration

Turn on Serializable UI Factory

[Required]

To use ZK in a clustering environment, you have to use the serializable UI factory. It could be done by specifying the following statement in WEB-INF/zk.xml:

<zk>
	<system-config>
		<ui-factory-class>org.zkoss.zk.ui.http.SerializableUiFactory</ui-factory-class>
	</system-config>
</zk>

SerializableUiFactory is the UI factory that will instantiate serializable sessions such that the sessions, components, pages and desktops will be serialized when a session is about to deactivate.

Turn on ClusterSessionPath for WebLogic and GAE

[Required if WebLogic and GAE][No need for other servers]
[Since 5.0.8]

WebLogic clustering server and GAE (Google App Engine) minimize the synchronization of the session states by assuming nothing has changed, if no session attribute has been modified in a HTTP request. Thus, you have to specify the following configuration in WEB-INF/zk.xml to enforce the server to synchronize the states for each Ajax request.

<zk>
	<listener>
		<listener-class>org.zkoss.zkplus.cluster.ClusterSessionPatch</listener-class>
	</listener>
</zk>

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Under the hub: ClusterSessionPatch is an ExecutionCleanup listener that updates an session attribute holding Session for each request.

Additional settings for JBoss

[Required if JBoss]

• According to JBoss' tutorial, additional settings are required if you are using JBoss server for clustering. Add the following settings in WEB-INF/web.xml to tell JBoss that you wish to cluster your web app.

<?xml version="1.0"?>
<web-app  xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    version="2.5">
    
    <distributable/>

</web-app>

• Create jboss-web.xml file under WEB-INF folder if fileupload' component is used in your app.

<jboss-web>
    <context-root>warFileName</context-root> <!-- context-root should be the same with war file name -->    
    <replication-config>
        <cache-name>standard-session-cache</cache-name>
        <replication-trigger>SET_AND_GET</replication-trigger>
        <replication-granularity>SESSION</replication-granularity>
        <replication-field-batch-mode>true</replication-field-batch-mode>
        <use-jk>true</use-jk>
        <max-unreplicated-interval>30</max-unreplicated-interval>
        <snapshot-mode>INSTANT</snapshot-mode>
        <snapshot-interval>1000</snapshot-interval>
    </replication-config>
    <max-active-sessions>5</max-active-sessions>
    <passivation-config>
        <use-session-passivation>true</use-session-passivation>
        <passivation-min-idle-time>60</passivation-min-idle-time>
        <passivation-max-idle-time>600</passivation-max-idle-time>
    </passivation-config>
</jboss-web>

Turn on Log

[Optional]

If an attribute or a listener is not serializable, ZK will skip it, i.e., not to serialize it (similar to how a Servlet container serializes the attributes of sessions). It is sometimes hard to know what are ignored, since it is common for a developer to forget to declare a value or a listener as serializable.

To detect this problem, you could turn on the logger for org.zkoss.io.serializable to the DEBUG level. The logger is the standard logger. You could consult the configuration of the Web server you use. Or, you could run the following statement when your application starts.

org.zkoss.util.logging.Log.lookup("org.zkoss.io.serializable").setLevel("DEBUG");

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Disable the Use of zscript

[Optional]
[since 5.0.8]

The interpreter (BeanShell) does not work well under the clustering environment, since the serializationis not stable. Thus, it is suggested to disable the use of zscript with the following statement. It is optional, but, by disabling, it is easy to prevent any possible use.

<system-config>
	<disable-zscript>true</disable-zscript>
</system-config>

Configuration Not Allowed

Here are a list of configuration that can not be used in the clustering environment. They are disabled by default. However, it is worth to double check if any of your members enables it accidentally.

Event Processing Thread

Do not enable the event processing thread. The event processing thread might be suspended, while the (suspended) thread cannot be migrated from one machine to another.

It is disabled by default. For more information, please refer to the Event Threads section.

Global Desktop Cache

Do not use GlobalDesktopCacheProvider (global desktop cache). The global desktop cache is stored in the servlet context, while only the data stored in sessions are migrated when failover takes place.

The desktop desktop cache is not used by default. Just make sure you don't configure it wrong.

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Version History

Version	Date	Content
5.0.7	April 2011	The log called org.zkoss.io.serializable was introduced.
5.0.8	June 2011	The listener called org.zkoss.zkplus.cluster.ClusterSessionPatch was introduced.