Integrating external components

In these sections, we will discuss how to make Cascading interoperate with external systems. Interoperation is an important aspect of "shoe-horning" a new technology into an existing infrastructure. Additionally, new technologies are emerging almost daily now, so using these capabilities in Cascading is important when migrating or evolving systems.

Flow and cascade events

Each flow and cascade has the ability to execute callbacks via an event listener. This ability is useful when an external application needs to be notified that either a flow or cascade has started, halted, completed, or thrown an exception. Flows and cascades generate events that can be handled by your client-side code.

Tip

For instance, at the completion of a flow that runs on an Amazon EC2 Hadoop cluster, an Amazon SQS message can be sent to notify another application to fetch the job results from S3 or begin the shutdown of the cluster that you are paying for.

1. These events are managed by a...