Request/reply patterns

Dealing with a messaging system often means using a one-way asynchronous communication; publish/subscribe is a perfect example.

One-way communications can give us great advantages in terms of parallelism and efficiency, but alone they are not able to solve all our integration and communication problems. Sometimes, a good old request/reply pattern might just be the perfect tool for the job. Therefore, in all those situations where an asynchronous one-way channel is all that we have, it's important to know how to build an abstraction that allows us to exchange messages in a request/reply fashion. That's exactly what we are going to learn next.

Correlation identifier

The first request/reply pattern we are going to learn is called correlation identifier and it represents the basic block for building a request/reply abstraction on top of a one-way channel.

The pattern consists in marking each request with an identifier, which is then attached to the response by the receiver...