FAQs of clustering

Q1. How to migrate from local to the cluster mode?

If you intend to migrate your production system from local (non-cluster) to the cluster mode, follow these steps:

1. Update the configuration to the cluster mode as explained above on your main server.

2. Use the same configuration on other cluster nodes.

3. Move the index and value storage to the shared file system.

4. Start the cluster.

Q2. Why is startup failed with the "Port value out of range" error?

On Linux, your startup is failed if you encounter the following error:

[INFO] Caused by: java.lang.IllegalArgumentException: Port value out of range: 65536

This problem happens under specific circumstances when JGroups-the networking library behind the clustering attempts to detect the IP to use for communication with other nodes.

You need to verify:

The host name is a valid IP address, served by one of the network devices, such as eth0, eth1.

The host name is NOT defined as localhost or 127.0.0.1.

Q3. How to solve the "failed sending message to null" error?

If you encounter the following error when starting up in the cluster mode on Linux:

Dec 15, 2010 6:11:31 PM org.jgroups.protocols.TP down
SEVERE: failed sending message to null (44 bytes)
java.lang.Exception: dest=/228.10.10.10:45588 (47 bytes)

Be aware that clustering on Linux only works with IPv4. Therefore, when using a cluster under Linux, add the following property to JVM parameters:

 -Djava.net.preferIPv4Stack=true

Q3. How to hide JGroups protocol warnings in the log?

In cluster mode several Platform subsystems, such as JCR, various caches, organization service, use shared JGroups transport. And in case of used by default UDP transport it might cause a side effect - lot of warnings, like these below:

WARNING: discarded message from different group "gatein-idm-api-cluster" (our group is "gatein-idm-store-cluster"). Sender was 192.168.1.55:54232
Dec 16, 2011 4:46:09 PM org.jgroups.protocols.TP passMessageUp
WARNING: discarded message from different group "gatein-idm-store-cluster" (our group is "gatein-idm-api-cluster"). Sender was 192.168.1.55:63364
Dec 16, 2011 4:46:10 PM org.jgroups.protocols.TP passMessageUp

To hide such warnings need configure the Application Server logger in appropriate way:

Apache Tomcat, in ${CATALINA_HOME}/conf/logging.properties add following lines

org.jgroups.level = SEVERE
org.jgroups.handlers = java.util.logging.ConsoleHandler,6gatein.org.apache.juli.FileHandler

JBoss Application Server, for server profile all, add in ${jboss_server}/server/all/conf/jboss-log4j.xml following

  <category name="org.jgroups.protocols.UDP">
    <priority value="ERROR"/>
  </category>