Event Notification

Each cluster job, or Flow, has the ability to execute callbacks via an event listener. This is very useful when external application need to be notified that a Flow has completed.

A good example is when running Flows on an Amazon EC2 Hadoop cluster. After the Flow is completed, a SQS event can be sent notifying another application it can now fetch the job results from S3. In tandem, it can start the process of shutting down the cluster if no more work is queued up for it.

Listeners listen for the following four events; starting, stopping, completed, and the catching of an Exception from the job.