Brokers, Contractors and Queues

The publication broker, publication contractor, and subscription contractor services are the primary application server elements required for asynchronous messaging. The publication broker service routes the workload to both contractor server processes.

This example illustrates the publication broker service routing the workload the contractor server processes.

Term	Definition
Publication broker	Acts as the routing mechanism. When an asynchronous service operation arrives in its queue, the publication broker service runs the defined routing rules. If the service operation needs to be published to a remote node, it routes the service operation to the publication contractor service. If the service operation is subscribed to on the local node, then the publication broker routes the service operation to the subscription contractor service. Routing involves submitting either a subscription or publication contract to the appropriate contractor, followed by an asynchronous call to the contractor service notifying it that work is waiting in the queue.
Publication contractor	References the publication contract submitted by the publication broker service and performs an HTTP post of the publication service operation to the integration gateway. When the integration gateway sends a reply indicating that it received the publication service operation, the publication contractor service updates the publication contract with the status of subscription processing (Done or Retry).
Subscription contractor	References the subscription contract submitted by the publication broker service and runs the appropriate notification PeopleCode. Then it updates the subscription contract concerning the status of the subscription processing.