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Chapter 33. How to write a monitoring framework

33.1. What is a monitoring framework?
33.2. Writing a monitoring framework
33.3. Monitoring frameworks and resource events
33.4. Using a monitoring framework

33.1. What is a monitoring framework?

A monitoring framework in OGSA-DAI monitors events emitted by activities and pipes during execution of a request by the activity framework. For example, a monitoring framework could be created to monitor data flow during the execution of a request and display progress graphically. A monitoring framework could be used for auditing or debugging purposes.

Monitoring frameworks implement the: 

uk.org.ogsadai.monitoring.MonitoringFramework

interface. This interface supports the following operations: 

  • public void registerListeners(RequestDescriptor requestDescriptor, 
                              OGSADAIRequestConfiguration requestContext);
    Register listeners on a given request context. This method allows the monitoring framework to register different listeners depending on both the actual request itself and the context of the request.

A request context of type OGSADAIRequestConfiguration provides two methods that can be used by the monitoring framework to register coponents that will listen for events from the activity framework.

  • registerActivityListener - activity listeners implement the uk.org.ogsadai.activity.event.ActivityListener interface and, when registered in the request context with this method, are notified of events that occur during the processing of an activity.
  • registerPipeListener - pipe listeners implement the uk.org.ogsadai.activity.event.PipeListener interface and are notified of pipe events such as when a block is written or read, and when the pipe is closed, terminated or an error occurred.

Depending upon the implementation of the monitoring framework it could register other components that implement either or both of ActivityListener and PipeListener interfaces or it could also implement these interfaces itself and handle the actual events itself.

OGSA-DAI, by default, distributes the following class that implements the MonitoringFramework interface: 

uk.org.ogsadai.monitoring.NullMonitoringFramework

which does not register any listeners.

33.2. Writing a monitoring framework

To write an OGSA-DAI monitoring framework you need to provide an implementation of the interface: 

uk.org.ogsadai.monitoring.MonitoringFramework

You will need to make the following decisions:

  • Which activity and pipe listeners are registered. This may depend on the request and the request context for example if the request is synchronous or asynchronous, or which user submitted the request.
  • What configuration your monitoring framework needs and how this is provided e.g. via values assumed to be in the OGSA-DAI context and provided via specific configuration properties (e.g. see Section 18.9, “Miscellaneous objects” or via setter methods on your monitoring framework (e.g. see Section 18.9.2, “External information on JNDI”).

A monitoring framework will usually provide its own implementations of activity listeners and pipe listeners which process activity and pipe events as required. The framework creates and registers listeners as appropriate. To make implementations of listeners available you need to place the the listener classes available to the OGSA-DAI server as a JAR file.

33.3. Monitoring frameworks and resource events

A further option is for the monitoring framework to register listeners that implement the uk.org.ogsadai.resource.event.ResourceManagerEventListener interface with the OGSA-DAI resource manager. The OGSA-DAI resource manager can be acquired from the OGSA-DAI context (see Section G.2, “OGSA-DAI context”) via the following code: 

OGSADAIContext context = OGSADAIContext.getInstance();
ResourceManager manager = context.getResourceManager();
manager.addResourceManagerEventListener(myComponent);

These listeners will then be informed whenever OGSA-DAI resources are added to or removed from the OGSA-DAI resource manager. This can be useful for monitoring the creation and removal of session, request, data source, data sink and data resources.

33.4. Using a monitoring framework

Once a monitoring framework has been written an OGSA-DAI server can be configured to use the framework to register listeners on the request context and perform other monitoring tasks as described.

A monitoring framework may be specified as part of the JNDI configuration but this is optional. If the OGSA-DAI server can access in its OGSADAI context a monitoring framework with ID uk.org.ogsadai.MONITORING_FRAMEWORK and which implements the interface uk.org.ogsadai.monitoring.MonitoringFramework then it will load and use this monitoring framework. If no monitoring framework is specified then the default uk.org.ogsadai.monitoring.NullMonitoringFramework is created and used.

Section 18.9, “Miscellaneous objects” describes how to add miscellaneous objects to the OGSA-DAI context.

  • Add a JNDI entry as shown below. Change the class in the type attribute of the JNDI entry for the monitoring framework to specify the class of the monitoring framework you want to use.
  • Add the JAR containing the monitoring framework including any new activity and pipe listeners to the specified directory.

The following example shows a JNDI configuration if your monitoring framework implementation was called com.example.LoggingMonitoringFramework.

In OGSA-DAI GT the monitoring framework is declared as follows: 

<resource name="ogsadai/misc/uk.org.ogsadai.MONITORING_FRAMEWORK"
           type="com.example.LoggingMonitoringFramework">
  <resourceParams>
    <parameter>
      <name>factory</name>
      <value>org.globus.wsrf.jndi.BeanFactory</value>
    </parameter>
  </resourceParams>
</resource>
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