Designing Event-Driven Systems

Chapter 6. Processing Events with Stateful Functions

Imperative styles of programming are some of the oldest of all, and their popularity persists for good reason. Procedures execute sequentially, spelling out a story on the page and altering the program’s state as they do so.

As mainstream applications became distributed in the 1980s and 1990s, the same mindset was applied to this distributed domain. Approaches like Corba and EJB (Enterprise JavaBeans) raised the level of abstraction, making distributed programming more accessible. History has not always judged these so well. EJB, while touted as a panacea of its time, fell quickly by the wayside as systems creaked with the pains of tight coupling and the misguided notion that the network was something that should be abstracted away from the programmer.

In fairness, things have improved since then, with popular technologies like gRPC and Finagle adding elements of asynchronicity to the request-driven style. But the application of this mindset to the design of distributed systems isn’t necessarily the most productive or resilient route to take. Two styles of programming that better suit distributed design, particularly in a services context, are the dataflow and functional styles.

You will have come across dataflow programming if you’ve used utilities like Sed or languages like Awk. These are used primarily for text processing; for example, a stream of lines might be pushed through a regex, one line at a time, with the output ...