When we talk about Message Exchange Patterns, or MEPs, we're considering the direction and timing of data between the client and service. How do I get into the bus and what are the implications of those choices? Let's discuss the four primary options.
This is probably the pattern that's most familiar to you. We're all comfortable making a function call to a component and waiting for a response. When a service uses this pattern, it's frequently performing a Remote Procedure Call where the caller accesses functionality on the distant service and is blocked until either a timeout occurs or until the receiver sends a response that is expected by the caller.
As we'll see below, while this pattern may set developers at ease, it may encourage bad behavior. Nevertheless, the cases where request/response services make the most sense are fine-grained functions and mashup services. If you need a list of active contracts that a hospital...