Tomcat – Is Tomcat Shared Session / Cluster between two machine possible

clustersessiontomcat

I have a setup of several Tomcat servers distributed between a few servers, all running the same thing. Apache is on top of Apache and a loadbalancer in front of the Apache servers. I want to cluster the Tomcats using Shared Session to minimize downtime and user interruption while deploying apps.

I know clustering works within the same server but is it possible to setup Tomcat in a way that it shares sessions between servers on different machines?

=> Server 1
==> Apache 1
===> Tomcat 1

=> Server 2
==> Apache 2
===> Tomcat 2

When Server/Tomcat 1 would be taken down, users and their sessions would transfer over to Server/Tomcat 2 and vice versa.

Best Answer

Take a look at Teracotta for web sessions.

Use Terracotta's fast, reliable web sessions plugin to get the scalability benefits of a stateless web architecture without overloading your database or rewriting your application. Terracotta for Sessions works with your favorite web framework and your own custom session objects.

The web sessions tutorial lists five simple steps for you to make in order to evaluate the product ( FOSS ).

Related Solutions

Tomcat – Running two independent tomcats on one machine, instead of one tomcat with multiple instances

Yes, we do this frequently.

Basically our approach (on Windows) is:

Ensure the full JDK is installed (Tomcat batch files require this)
Download and Tomcat (6.1.20) - the zip version, not the windows installer.
Unzip to a folder named for the purpose of the Tomcat instance (eg to C:\Tomcat6_SW for SuperWEB 1)
Copy the unzipped files to other folders for the other required instances (eg C:\Tomcat6_SW2, C:\Tomcat6_SV)
For each instance, edit server.xml so that there are no port conflicts
For each instance:
- a. Edit startup.bat to explicitly define CATALINA_HOME and JAVA_HOME
- b. Rename startup.bat to reflect the purpose of the Tomcat instance, for instance SWstartup.bat for SuperWEB1
- c. Edit service.bat as above to explicitly define CATALINA_HOME and JAVA_HOME
- d. Run service.bat to create a Windows service with a service name and description for this Tomcat instance. The service name must be unique, and cannot contain spaces.
- e. Rename the tomcat6w.exe file to the name of the service that you have created (for instance, if the service name is SWEB1Tomcat, tomcat6w.exe should be renamed to SWEB1Tomcat.exe). If this is not done, the tomcat6w.exe application will not refer to the correct service.
- f. Run the renamed application and set service properties as follows:
  - 1. set any Java options required in the Java tab
  - 1. set the startup type to Automatic
  - 1. IMPORTANT: change the Log On account to other than “Local System account”, ie something with a lower privilege level.

(Note that you may want to create separate setenv.bat files for each instance.

Tomcat Cluster – Farm Deployer Not Working in Tomcat Cluster

The first location you should take a look at is catalina.out, it will tell you what might be wrong.

If you can't make it works with multicast, just try static membership (I think it will simpler).

Below is my config:

Put the <Cluster node inside the <Host element:

<Engine name="Catalina" defaultHost="localhost" jvmRoute="tomcat1">         
  <Host name="localhost"  appBase="webapps"
            unpackWARs="true" autoDeploy="true"
            xmlValidation="false" xmlNamespaceAware="false">

    <Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster">
        <Channel className="org.apache.catalina.tribes.group.GroupChannel">
            <Receiver className="org.apache.catalina.tribes.transport.nio.NioReceiver"
                  address="192.168.5.149"
                  port="4000"
                  selectorTimeout="100"
                  maxThreads="6"/>
            <Interceptor className="org.apache.catalina.tribes.group.interceptors.TcpFailureDetector"/>
            <Interceptor className="org.apache.catalina.tribes.group.interceptors.StaticMembershipInterceptor">
                <Member className="org.apache.catalina.tribes.membership.StaticMember"
                      port="4001"
                      securePort="-1"
                      host="192.168.5.199"
                      domain="staging-cluster"
                      uniqueId="{0,1,2,3,4,5,6,7,8,9}"/>
            </Interceptor>
        </Channel>
        <Deployer className="org.apache.catalina.ha.deploy.FarmWarDeployer"
            tempDir="/usr/share/tomcat6/tempdir/"
            deployDir="/usr/share/tomcat6/webapps/"
            watchDir="/usr/share/tomcat6/watchdir/"
            watchEnabled="true"/>
    </Cluster>
  </Host>
</Engine>

The address attribute in <Receiver element is the node1's IP address. (in your case is .101)
The port is listening for replication messages on node 1 (4000-4100)
The Member's port in <Interceptor is listening for cluster messages on node 2
The Member's host is the IP address of node 2 (.102)

server.xml on the node 2:

    <Cluster className="org.apache.catalina.ha.tcp.SimpleTcpCluster">
        <Channel className="org.apache.catalina.tribes.group.GroupChannel">
            <Receiver className="org.apache.catalina.tribes.transport.nio.NioReceiver"
                  address="192.168.5.199"
                  port="4001"
                  selectorTimeout="100"
                  maxThreads="6"/>
            <Interceptor className="org.apache.catalina.tribes.group.interceptors.TcpFailureDetector"/>
            <Interceptor className="org.apache.catalina.tribes.group.interceptors.StaticMembershipInterceptor">
                <Member className="org.apache.catalina.tribes.membership.StaticMember"
                      port="4000"
                      securePort="-1"
                      host="192.168.5.149"
                      domain="staging-cluster"
                      uniqueId="{0,1,2,3,4,5,6,7,8,9}"/>
            </Interceptor>
        </Channel>
        <Deployer className="org.apache.catalina.ha.deploy.FarmWarDeployer"
            tempDir="/usr/share/tomcat6/tempdir/"
            deployDir="/usr/share/tomcat6/webapps/"
            watchDir="/usr/share/tomcat6/watchdir/"
            watchEnabled="false"/>
    </Cluster>

Make sure that Tomcat can write to tempDir and watchDir folder:

chmod g+w tempDir watchDir
chgrp tomcat tempDir watchDir

If you don't do this, you will get the below error:

Aug 13, 2011 10:28:33 PM org.apache.catalina.ha.deploy.FarmWarDeployer messageReceived
SEVERE: Unable to read farm deploy file message.
java.io.IOException: Permission denied

Remember to add <distributable/> into webapps/ROOT/WEB-INF/web.xml:

<web-app xmlns="http://java.sun.com/xml/ns/javaee"
  ...
  <display-name>Welcome to Tomcat</display-name>
  <description>
     Welcome to Tomcat
  </description>
  <distributable/>
</web-app>

Whenever you copy a .war file into watchdir folder on node 1, you will see something like the following in catalina.out:

Aug 14, 2011 1:40:58 AM org.apache.catalina.ha.deploy.WarWatcher check
INFO: check cluster wars at /usr/share/tomcat6/watchdir
Aug 14, 2011 1:40:59 AM org.apache.catalina.ha.deploy.FarmWarDeployer fileModified
INFO: Installing webapp[/cas] from /usr/share/tomcat6/webapps/cas.war
Aug 14, 2011 1:40:59 AM org.apache.catalina.ha.deploy.FarmWarDeployer remove
INFO: Cluster wide remove of web app /cas
Aug 14, 2011 1:40:59 AM org.apache.catalina.startup.HostConfig deployWAR
INFO: Deploying web application archive cas.war

and on the node 2:

Aug 14, 2011 1:40:59 AM org.apache.catalina.startup.HostConfig deployWAR
INFO: Deploying web application archive cas.war

Good luck!

Best Answer

Related Solutions

Tomcat – Running two independent tomcats on one machine, instead of one tomcat with multiple instances

Tomcat Cluster – Farm Deployer Not Working in Tomcat Cluster

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