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Jonas Bonér

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This is the foreword I wrote for Roland Kuhn’s excellent book on Reactive Design Patterns.

Available from Manning here.


I’m grateful that Roland has taken the time to write this foundational book, and I can’t think of anyone more capable of pulling it off. Roland is an unusually clear and deep thinker; he coauthored the Reactive Manifesto, has been the technical lead for the Akka project for several years, has coauthored and taught the very popular Coursera course on Reactive programming and design, and is the best technical writer I have met.

Clearly, I’m very excited about this book. It outlines what Reactive architecture/design is all about, and does an excellent job explaining it from first principles in a practical context. Additionally, it is a catalog of patterns that explains the bigger picture, how to think about system design, and how it is all connected—much like what Martin Fowler’s Patterns of Enterprise Application Architecture did 15 years ago.

During my professional life, I have seen the immense benefits of resilient, loosely coupled, message-driven systems firsthand, especially when compared with more traditional approaches that propose to hide the nature of distributed systems. In 2013, I had the idea of formalizing the experiences and lessons learned: the Reactive Manifesto was born. It started out as a set of rough notes that I remember presenting to the company at one of Typesafe’s (now Lightbend) internal technical meetups. Coincidentally, this meetup was collocated with the Scala Days New York conference, where Roland, Martin Odersky, and Erik Meijer shot their bad, and unintentionally quite funny, promotion video of their Coursera course on Reactive programming. The story around the Reactive principles resonated with the other engineers and was published in July of 2013. Since then, the Manifesto has been receiving a lot of great feedback from the community. It was rewritten and vastly improved by Roland, Martin Thompson, Dave Farley, and myself, leading up to version 2.0 published in September 2014. By the end of 2016, it had been signed by more than 17,000 people. During this time, we have seen Reactive progress from a virtually unacknowledged technique used only by fringe projects within a select few corporations to a part of the overall platform strategy of numerous big players in many different fields, including middleware, financial services, retail, social media, betting/gaming, and so on.

The Reactive Manifesto defines Reactive Systems as a set of architectural design principles that are geared toward meeting the demands that systems face—today and tomorrow. These principles are most definitely not new; they can be traced back to the ’70s and ’80s and the seminal work by Jim Gray and Pat Helland on the Tandem System, as well as Joe Armstrong and Robert Virding on Erlang. However, these pioneers were ahead of their time, and it was not until the past five years that the technology industry was forced to rethink current best practices for enterprise system development and learned to apply the hard-won knowledge of the Reactive principles to today’s world of multicore architectures, Cloud Computing, and the Internet of Things.

By now, the Reactive principles have had a big impact on the industry, and as with many successful ideas, they get overloaded and reinterpreted. This is not a bad thing; ideas need to evolve to stay relevant. However, this can also cause confusion and lead to dilution of the original intent. One example is the unfortunate emerging misconception that Reactive is nothing but programming in an asynchronous and nonblocking style using callbacks or stream-oriented combinators—techniques that are aptly classified as Reactive Programming. Concentrating on this aspect alone means missing out on many of the benefits of the Reactive principles. It is the contribution of this book to take a much larger perspective—a systems view—moving the focus from how individual components function in isolation to the design of collaborative, resilient, and elastic systems: Reactive Systems.

This future classic belongs on the shelf of every professional programmer, right next to GoF and Domain-Driven Design. Enjoy the ride—I certainly did!

—Jonas Bonér, Founder and CTO of Lightbend, Creator of Akka