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Proof Of Concept

  • This is a functional proof of concept, please feel free to try it out and also post comments, suggestions, etc.

Information

The JMS event service is meant to be a replacement for the current Event Service which uses the database to send messages between nodes in the cluster. It allows for a standard message sending methodology and does not touch the database. Events are also transactional with JMS.

JMS Information

JMS Event Service

  • Goals
    • Standard message types (JMS Message)
    • Better cluster wide events with lower database load and more flexibility
    • More flexible message data (JMS supports all kinds of data being attached to messages)
    • Easy interception of events (via standard JMS listeners)
    • Easy handling of custom event queues
    • Encourage wider usage of events in Sakai
  • Allows JMS and event handling in Sakai
    • Lei (a student worker here at CARET) and I have created a general JMS service for Sakai and an implementation of the Sakai event tracking
      service to go along with it
    • Our current JMS implementation uses ActiveMQ and auto discovery to send messages to other Sakai servers running in the cluster
  • Uses some sakai.properties for config (but works with defaults)
    • Requires users to disable the legacy EventTrackingService
    • Also requires allowing the JMS api into shared (already there in trunk)
  • Benefits in a little more detail
    • Reduce the load that the legacy cluster event service puts on the DB
    • Able to use JMS messages
    • Easy to define standard listeners
      • Allows you to add a listener or listeners that can log to a db on a different machine or wherever else you want without impacting the production database instance
    • ability to set up your own message destinations
    • ability to send just about anything in your message (JMS allows full objects and all kinds of crazy stuff)
    • transactional message processing
    • ability to control where the messages go (local only, cluster, etc.)
  • Code https://source.sakaiproject.org/contrib/messageservice/trunk
  • JIRA SAK issue for tracking this: http://jira.sakaiproject.org/jira/browse/SAK-11021

Deploying and Running The JMS Event Service in sakai_2-5-x

Getting the source and building it

  • svn co https://source.sakaiproject.org/svn/sakai/branches/sakai_2-5-x
    cd sakai_2-5-x
    https://source.sakaiproject.org/contrib/messageservice/trunk messageservice
    mvn clean install sakai:deploy
    

Sakai Properties

Property

Default Value

Comments

jms.useJMX

false

If you have tomcat configured to allow JMX access, I would recommend to enable this setting as it greatly helps during the development process

jms.brokerURL

tcp://localhost:61616

-

jms.brokerDataPath

sakai-home location

This is either in "tomcat/sakai" or the location defined by JAVA_OPTS "-Dsakai.home=/path/to/sakai-home/"

Troubleshooting

  • If tomcat doesn't start completely and the last message in catalina.out is the following:
    • WARN: brokerName not set (2007-12-11 20:22:26,149 main_org.apache.activemq.transport.discovery.multicast.MulticastDiscoveryAgent)
      
      ... then, you probably have some port/transport security service in place such at iptables. The issue is that activeMQ uses UDP on port 6155 for its multicast discovery. This webpage has some information regarding this topic.
    • So in my case, I had to add the following line to my iptables
      • -A RH-Firewall-1-INPUT -m state --state NEW -m udp -p udp -s 192.168.1.0/24 --dport 6155 -j ACCEPT
        
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