Enterprise Integration Patterns: Designing, Building, and Deploying Messaging Solutions (Addison-Wesley Signature Series (Fowler))

by Hohpe Gregor

An incoming message initializes the Process Manager. We call this message the trigger message. Based on the rules inside the Process Manager, it sends a message (1) to the first processing step, implemented by Processing Unit A. After unit A completes its task, it sends a reply message back to the Process Manager. The Process Manager determines the next step to be executed and sends a message (2) to the next processing unit. As a result, all message traffic runs through this central “hub,” hence the term hub-and-spoke. The downside of this central control element is the danger of turning the Process Manager into a performance bottleneck.