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

by Hohpe Gregor

Reliable Communication. Messaging provides reliable delivery that an RPC cannot. The reason messaging is more reliable than RPC is that messaging uses a store-and-forward approach to transmitting messages. The data is packaged as messages, which are atomic, independent units. When the sender sends a message, the messaging system stores the message. It then delivers the message by forwarding it to the receiver’s computer, where it is stored again. Storing the message on the sender’s computer and the receiver’s computer is assumed to be reliable. (To make it even more reliable, the messages can be stored to disk instead of memory; see Guaranteed Delivery [122].) What is unreliable is forwarding (moving) the message from the sender’s computer to the receiver’s computer, because the receiver or the network may not be running properly. The messaging system overcomes this by resending the message until it succeeds. This automatic retry enables the messaging system to overcome problems with the network so that the sender and receiver don’t have to worry about these details.