In Chapter 4, “Working System,” we built a basic restaurant ordering system; we did it focusing on the communication topologies and not on how the components should have been properly designed one by one. This was a deliberately stripped-down design that focused more on how services talked to each other (using NATS) than on how they were structured internally. It worked, but it was never meant to be production-grade. In this chapter, we revisit one of its most important pieces: the Order Processor. And this time, we’re doing it properly, following the principles about DDD and hexagonal architecture learned in the previous chapters of this part.