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Jetty Based Web Session Replication



image NOTE: This feature is supported for Hazelcast Enterprise 3.4 or higher.

Sample Code: Please see our sample application for Jetty Based Web Session Replication.

Overview

Jetty Web Session Replication with Hazelcast Enterprise is a container specific module that enables session replication for JEE Web Applications without requiring changes to the application.

Features

  1. Jetty 7 & 8 & 9 support
  2. Support for sticky and non-sticky sessions
  3. Jetty failover
  4. Deferred write for performance boost
  5. Client/Server and P2P modes
  6. Declarative and programmatic configuration

Supported Containers

Jetty Web Session Replication Module has been tested against the following containers.

  • Jetty 7 - It can be downloaded here.
  • Jetty 8 - It can be downloaded here.
  • Jetty 9 - It can be downloaded here.

Latest tested versions are 7.6.16.v20140903, 8.1.16.v20140903 and 9.2.3.v20140905

Requirements

  • Jetty instance must be running with Java 1.6 or higher.
  • Session objects that need to be clustered have to be Serializable.
  • Hazelcast Jetty-based Web Session Replication is built on top of the jetty-nosql module. This module (jetty-nosql-<*jettyversion*>.jar) needs to be added to $JETTY_HOME/lib/ext. This module can be found here.

How Jetty Session Replication Works

Jetty Session Replication in Hazelcast Enterprise is a Hazelcast Module where each created HttpSession Object's state is kept in Hazelcast Distributed Map.

Since the session data are in Hazelcast Distributed Map, you can use all the available features offered by Hazelcast Distributed Map implementation, such as MapStore and WAN Replication.

Jetty Web Session Replication runs in two different modes:

  • P2P: all Jetty instances launch its own Hazelcast Instance and join to the Hazelcast Cluster and,
  • Client/Server: all Jetty instances put/retrieve the session data to/from an existing Hazelcast Cluster.

P2P (Peer-to-Peer) Deployment

P2P deployment launches embedded Hazelcast Node in each server instance.

Features

This type of deployment is simple: just configure your Jetty and launch. There is no need for an external Hazelcast cluster.

Sample P2P Configuration to use Hazelcast Session Replication

  • Go to hazelcast.com and download the latest Hazelcast Enterprise.
  • Unzip the Hazelcast Enterprise zip file into the folder $HAZELCAST_ENTERPRISE_ROOT.
  • Update $HAZELCAST_ENTERPRISE_ROOT/bin/hazelcast.xml with the provided Hazelcast Enterprise License Key.
  • Put hazelcast.xml in the folder $JETTY_HOME/etc.
  • Put $HAZELCAST_ENTERPRISE_ROOT/lib/hazelcast-enterprise-all-<version>.jar, $HAZELCAST_ ENTERPRISE_ROOT/lib/hazelcast-enterprise-<jettyversion>-<version>.jar in the folder $JETTY_HOME/lib/ext.
  • Configure Session ID Manager and Session Manager. Please see the following explanations for configuring these managers.

Configuring the HazelcastSessionIdManager

You need to configure a com.hazelcast.session.HazelcastSessionIdManager instance in jetty.xml. Add the following lines to your jetty.xml.

<Set name="sessionIdManager">
    <New id="hazelcastIdMgr" class="com.hazelcast.session.HazelcastSessionIdManager">
        <Arg><Ref id="Server"/></Arg>
        <Set name="configLocation">etc/hazelcast.xml</Set>
    </New>
</Set>

Configuring the HazelcastSessionManager

HazelcastSessionManager can be configured from a context.xml file. Each application has a context file in the $CATALINA_HOME$/contexts folder. You need to create this context file if it does not exist. The context filename must be the same as the application name, e.g. example.war should have a context file named example.xml.

The file context.xml should have the following content.

<Ref name="Server" id="Server">
    <Call id="hazelcastIdMgr" name="getSessionIdManager"/>
</Ref>
<Set name="sessionHandler">
    <New class="org.eclipse.jetty.server.session.SessionHandler">
        <Arg>
            <New id="hazelcastMgr" class="com.hazelcast.session.HazelcastSessionManager">
                <Set name="idManager">
                    <Ref id="hazelcastIdMgr"/>
                </Set>
            </New>
        </Arg>
    </New>
</Set>
  • Start Jetty instances with a configured load balancer and deploy the web application.

image NOTE: In Jetty 9, there is no folder with the name contexts. You have to put the file context.xml under the webapps directory. And you need to add the following lines to context.xml.

<Ref name="Server" id="Server">
    <Call id="hazelcastIdMgr" name="getSessionIdManager"/>
</Ref>
<Set name="sessionHandler">
    <New class="org.eclipse.jetty.server.session.SessionHandler">
        <Arg>
            <New id="hazelcastMgr" class="com.hazelcast.session.HazelcastSessionManager">
                <Set name="sessionIdManager">
                    <Ref id="hazelcastIdMgr"/>
                </Set>
            </New>
        </Arg>
    </New>
</Set>

Client/Server Deployment

In client/server deployment type, Jetty instances work as clients to an existing Hazelcast Cluster.

Features

  • Existing Hazelcast cluster is used as the Session Replication Cluster.
  • The architecture is completely independent. Complete reboot of Jetty instances without losing data.

Sample Client/Server Configuration to use Hazelcast Session Replication

  • Go to hazelcast.com and download the latest Hazelcast Enterprise.
  • Unzip the Hazelcast Enterprise zip file into the folder $HAZELCAST_ENTERPRISE_ROOT.
  • Update $HAZELCAST_ENTERPRISE_ROOT/bin/hazelcast.xml with the provided Hazelcast Enterprise License Key.
  • Put hazelcast.xml in the folder $JETTY_HOME/etc.
  • Put $HAZELCAST_ENTERPRISE_ROOT/lib/hazelcast-enterprise-all-<version>.jar, $HAZELCAST_ ENTERPRISE_ROOT/lib/hazelcast-enterprise-<jettyversion>-<version>.jar in the folder $JETTY_HOME/lib/ext.
  • Configure Session ID Manager and Session Manager. Please see below explanations for configuring these managers.

Configuring the HazelcastSessionIdManager

You need to configure a com.hazelcast.session.HazelcastSessionIdManager instance in jetty.xml. Add the following lines to your jetty.xml.

<Set name="sessionIdManager">
    <New id="hazelcastIdMgr" class="com.hazelcast.session.HazelcastSessionIdManager">
        <Arg><Ref id="Server"/></Arg>
        <Set name="configLocation">etc/hazelcast.xml</Set>
        <Set name="clientOnly">true</Set>
    </New>
</Set>

Configuring the HazelcastSessionManager

HazelcastSessionManager can be configured from a context.xml file. Each application has a context file under the $CATALINA_HOME$/contexts folder. You need to create this context file if it does not exist. The context filename must be the same as the application name, e.g. example.war should have a context file named example.xml.

    <Ref name="Server" id="Server">
        <Call id="hazelcastIdMgr" name="getSessionIdManager"/>
    </Ref>    
    <Set name="sessionHandler">
        <New class="org.eclipse.jetty.server.session.SessionHandler">
            <Arg>
                <New id="hazelMgr" class="com.hazelcast.session.HazelcastSessionManager">
                    <Set name="idManager">
                        <Ref id="hazelcastIdMgr"/>
                    </Set>
                </New>
            </Arg>
        </New>
    </Set>

image NOTE: In Jetty 9, there is no folder with name contexts. You have to put the file context.xml file under webapps directory. And you need to add below lines to context.xml.

    <Ref name="Server" id="Server">
        <Call id="hazelcastIdMgr" name="getSessionIdManager"/>
    </Ref>    
    <Set name="sessionHandler">
        <New class="org.eclipse.jetty.server.session.SessionHandler">
            <Arg>
                <New id="hazelMgr" class="com.hazelcast.session.HazelcastSessionManager">
                    <Set name="sessionIdManager">
                        <Ref id="hazelcastIdMgr"/>
                    </Set>
                </New>
            </Arg>
        </New>
    </Set>

  • Launch a Hazelcast Instance using $HAZELCAST_ENTERPRISE_ROOT/bin/server.sh or $HAZELCAST_ ENTERPRISE_ROOT/bin/server.bat.

  • Start Tomcat instances with a configured load balancer and deploy the web application.

Optional HazelcastSessionIdManager Parameters

HazelcastSessionIdManager is used both in P2P and Client/Server mode. Use the following parameters to configure the Jetty Session Replication Module to better serve your needs.

  • workerName: Set this attribute to a unique value for each Jetty instance to enable session affinity with a sticky-session configured load balancer.
  • cleanUpPeriod: Defines the working period of session clean-up task in milliseconds.
  • configLocation: specifies the location of hazelcast.xml.



Optional HazelcastSessionManager Parameters

HazelcastSessionManager is used both in P2P and Client/Server mode. Use the following parameters to configure Jetty Session Replication Module to better serve your needs.

  • savePeriod: Sets the interval of saving session data to the Hazelcast cluster. Jetty Web Session Replication Module has its own nature of caching. Attribute changes during the HTTP Request/HTTP Response cycle are cached by default. Distributing those changes to the Hazelcast Cluster is costly, so Session Replication is only done at the end of each request for updated and deleted attributes. The risk with this approach is losing data if a Jetty crash happens in the middle of the HTTP Request operation. You can change that behavior by setting the savePeriod attribute.

Notes:

  • If savePeriod is set to -2, HazelcastSessionManager.save method is called for every doPutOrRemove operation.
  • If it is set to -1, the same method is never called if Jetty is not shut down.
  • If it is set to 0 (the default value), the same method is called at the end of request.
  • If it is set to 1, the same method is called at the end of request if session is dirty.



Session Expiry

Based on Tomcat configuration or sessionTimeout setting in web.xml, the sessions are expired over time. This requires a cleanup on Hazelcast Cluster, since there is no need to keep expired sessions in it.

cleanUpPeriod, which is defined in HazelcastSessionIdManager, is the only setting that controls the behavior of session expiry policy in Jetty Web Session Replication Module. By setting this, you can set the frequency of the session expiration checks in the Jetty Instance.

Session Affinity

HazelcastSessionIdManager can work in sticky and non-sticky setups.

The clustered session mechanism works in conjunction with a load balancer that supports stickiness. Stickiness can be based on various data items, such as source IP address, or characteristics of the session ID, or a load-balancer specific mechanism. For those load balancers that examine the session ID, HazelcastSessionIdManager appends a node ID to the session ID, which can be used for routing. You must configure the HazelcastSessionIdManager with a workerName that is unique across the cluster. Typically the name relates to the physical node on which the instance is executed. If this name is not unique, your load balancer might fail to distribute your sessions correctly. If sticky sessions are enabled, the workerName parameter has to be set, as shown below.

<Set name="sessionIdManager">
    <New id="hazelcastIdMgr" class="com.hazelcast.session.HazelcastSessionIdManager">
        <Arg><Ref id="Server"/></Arg>
        <Set name="configLocation">etc/hazelcast.xml</Set>
        <Set name="workerName">unique-worker-1</Set>
    </New>
</Set>