The Workflow Broker (formerly "Ensemble Broker") is a GSI web service designed to manage large computational jobs on production hosts.
The broker is designed to be extensible with respect to
The extensions usually involve implementing one or more module types.
This service sends and receives events via a JMS message bus, and acts as a client to the Host Information Service in order to configure the payloads to run on specific resources. For its position in the more general service-infrastructure, see Services.
In order to run through the broker, a Workflow Description must be created and submitted (refer to the Siege pages for a walk-through of this process). This description in turn will contain one or more scripted payloads, which can run from trivial to very complex, depending on the nature of the work to be accomplished through a single job launched onto the host; however, no special changes or recompilation of the underlying computational codes is necessary.
Siege also allows the user to inspect the state of workflows which have been or are being processed and to view all the events published in connection with them; this is particularly useful for debugging purposes. Once again this can be done entirely asynchronously (i.e., one can disconnect and then, upon reconnecting, retrieve a historical view of the state of the workflow).