Tomcat clustering configuration
The following steps assume that you have installed a Tomcat 5.5.x bundle or latest, i only tested on 5.5.27 but is should work for other configuration as well. The network configuration apply to Linux and may vary with the distribution. It should work as is for distributions based on Red Hat.
For Tomcat clustering we have two main things to configure:
- Configure the network environment for clustering (open ports, add multicast route),
- Configure Tomcat clustering support.
Configure the network support for cluster
Opening Specific HTTP Ports (e.g. Port 45564, 4001)
The cluster class will start up a membership service (multicast) and a replication service (tcp unicast). See also http://www.cyberciti.biz/faq/howto-rhel-linux-open-port-using-iptables/ for a brief article on this. You will need to have root access as noted above to complete this.
Your server may or may not already have this entry. Open iptables:
> vi /etc/sysconfig/iptables
Add the following entries:
-A RH-Firewall-1-INPUT -p udp -m udp --dport 45564 -j ACCEPT -A RH-Firewall-1-INPUT -p tcp -m tcp --dport 45564 -j ACCEPT -A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 4001 -j ACCEPT
Save and close the above file and after restart the iptables
> /etc/init.d/iptables restart
Configure the multicast address and routes.
Clustering membership is established using very simple multicast pings. Each Tomcat instance will periodically send out a multicast ping, in the ping message the instance will broad cast its IP and TCP listen port for replication. If an instance has not received such a ping within a given timeframe, the member is considered dead.
Add routeĀ (the server’s ip address)
sudo /sbin/route add 228.0.0.4 gw 10.72.10.1 dev bond0
Edit rc.local to make the change persistent through restarts.
sudo vim /etc/rc.d/rc.local
Add this line at the end (the server’s ip address)
/sbin/route add 228.0.0.4 gw 10.72.10.1 dev bond0
Configure Tomcat to support clustering.
Application clustering with Tomcat has two steps:
- Enable clustering support,
- Make you application clusterizable.
Enable Tomcat clustering support
You need to enable the cluster support in Tomcat by editing the server.xml file. Open server.xml
sudo vim /usr/local/tomcat-5.5.27/conf/server.xml
Enable clustering configuration in the configuration file, notice that the default configuration is using the DeltaManager which will replicate only the session’s changes and not the entire object:
<Cluster className="org.apache.catalina.cluster.tcp.SimpleTcpCluster" managerClassName="org.apache.catalina.cluster.session.DeltaManager" expireSessionsOnShutdown="false" useDirtyFlag="true" notifyListenersOnReplication="true"> <Membership className="org.apache.catalina.cluster.mcast.McastService" mcastAddr="228.0.0.4" mcastPort="45564" mcastFrequency="500" mcastDropTime="3000"/> <Receiver className="org.apache.catalina.cluster.tcp.ReplicationListener" tcpListenAddress="10.72.10.1" tcpListenPort="4001" tcpSelectorTimeout="100" tcpThreadCount="6"/> <Sender className="org.apache.catalina.cluster.tcp.ReplicationTransmitter" replicationMode="pooled" ackTimeout="15000" waitForAck="true"/> <Valve className="org.apache.catalina.cluster.tcp.ReplicationValve" filter=".*\.gif;.*\.js;.*\.jpg;.*\.png;.*\.htm;.*\.html;.*\.css;.*\.txt;"/> <Deployer className="org.apache.catalina.cluster.deploy.FarmWarDeployer" tempDir="/tmp/war-temp/" deployDir="/tmp/war-deploy/" watchDir="/tmp/war-listen/" watchEnabled="false"/> <ClusterListener className="org.apache.catalina.cluster.session.ClusterSessionListener"/> </Cluster>
One main condition for replication to work is that your session content is serializable. Add a _jvmRoute_ to your Tomcat Engine section From
<Engine name="Catalina" defaultHost="localhost">
To
<Engine name="Catalina" defaultHost="localhost" jvmRoute="tomcat1">
jvmRoute identifies unique a Tomcat instance in a cluster. If multiple servers are used I recommend you to use descriptive names.
Make your application clusterizable
Configuring Tomcat clustering is not enough to cluster your application. For that you need to tell Tomcat which application you want to be clusterizable. This is achieved in two ways:
- by modifying the ROOT.xml (the context configuration file”
- by modifying the web.xml
Enable application clustering by ROOT.xml
Edit ROOT.xml file
sudo vim /usr/local/tomcat-5.5.27/conf/Catalina/localhost/ROOT.xml
Look for
<Context path="" cookies="true" distributable="true" crossContext="true">
Change it to
<Context path="" debug="0" reloadable="true" cookies="true" crossContext="false" privileged="false" >
Enable application clustering by editing the web.xml
Edit the web.xml file
sudo vim /usr/local/tomcat-5.5.27/webapps/ROOT/WEB-INF/web.xml
Look for:
<web-app xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd" version="2.4"> <context-param> <param-name>contextClass</param-name> .............
Change it to:
<web-app xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd" version="2.4"> <distributable/> <context-param> <param-name>contextClass</param-name> .............
Restart Tomcat
cd /usr/local/tomcat-5.5.27/bin/ sudo ./shutdown.sh sudo ./startup.sh or if you have a init script sudo /etc/init.d/tomcat5 restart
You need to configure all the nodes in the cluster as detailed above. Every node should have unique name provided by “jvmRoute” attribute.
Further reading
Cluster-howto | http://tomcat.apache.org/tomcat-5.5-doc/cluster-howto.html