Designing Reactive Systems

Chapter 5. Actors in an IoT Application

In this final chapter, let’s work through a more realistic example of using actors to implement features in a real-life system. In this example, we are responsible for building an Internet of Things (IoT) application, in which we currently have hundreds of thousands of devices that are monitored continuously (with the expectation of this to grow over time into the millions).

Each device periodically feeds status data back to the application over the Internet. We decide that we want to represent each device with an actor that maintains the state of the device in our system. When a message arrives over the Internet to our application the message somehow needs to be routed to the specific actor.

Our system then will have to support millions of these device actors. The good news is that actors are fairly lightweight (a default actor is only 500 bytes in size, compared to 1 million bytes for a thread), so they do not consume a lot of memory; however, in this case one node cannot handle the entire load. In fact, we do not want to run this application on a single node, we want to distribute the load across many nodes so as to avoid any bottlenecks or performance issues with our IoT application. Also, we want an architecture that can scale elastically as more devices come online, so the application must be able to scale horizontally across many servers as well as scale vertically on a single server.

As a result of these requirements, we decide to ...