In this chapter, you have learned about ZeroMQ as a new communication protocol and how you can use it in PHP. In contrast to HTTP, ZeroMQ supports other and more complex communication patterns than the simple request/reply pattern. Especially the publish/subscribe and the push/pull pattern, which allow you to build loosely coupled architectures that are easily extensible by new functionalities and scale very well.
You have also learned how you can use the ReactPHP framework to build asynchronous services using event loops and how you can make asynchronicity manageable using promises. We have also discussed how you can integrate ZeroMQ-based applications with regular HTTP APIs.
While the previous chapters have all focused on different network communication patterns (RESTful HTTP in Chapter 5, Creating a RESTful Web Service, WebSockets in Chapter 6, Building a Chat Application, and now ZeroMQ), we will make a fresh start in the following chapter and learn how PHP can be used to build...