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

by Hohpe Gregor

Each component in the system is now connected to two messaging subsystems: 1. The Application Message Flow 2. The Control Bus The application message flow transports all application-related messages. The components subscribe and publish to these channels just as they would in an unmanaged scenario. In addition, each component also sends and receives messages from the channels that make up the Control Bus. These channels connect to a central management component. The Control Bus is well suited to carry the following types of messages: 1. Configuration—Each component involved in the message flow should have configurable parameters that can be changed as required. These parameters include channel addresses, message data formats, timeouts, and so on. Components use the Control Bus rather than property files to retrieve this information from a central repository, allowing a central point of configuration and the reconfiguration of the integration solution at runtime. For example, the routing table inside a Content-Based Router (230) may need to be updated dynamically based on system conditions, such as overload or component failure. 2. Heartbeat—Each component may send a periodic heartbeat message on the Control Bus at specified intervals so that a central console application can verify that the component is functioning properly. This heartbeat may also include metrics about the component, such as number of messages processed and the amount of available memory on the machine. 3...