Akka is a Scala-based toolkit that simplifies developing concurrent distributed applications. Akka uses Actors-independently executing processes that communicate via message passing—as the foundation for fault-tolerant applications where individual actors can fail without crashing everything. Perfect for high-volume applications that need to scale rapidly, Akka is an efficient foundation for event-driven systems that want to scale elastically up and out on demand, both on multi-core processors and across server nodes. Akka in Action is a comprehensive tutorial on building message-oriented systems using Akka. The book takes a hands-on approach, where each new concept is followed by an example that shows you how it works, how to implement the code, and how to (unit) test it. You'll learn to test and deploy an actor system and scale it up and out, showing off Akka's fault tolerance. As you move along, you'll explore a message-oriented event-driven application in Akka. You'll also tackle key issues like how to model immutable messages and domain models, and apply patterns like Event Sourcing, and CQRS. The book concludes with practical advice on how to tune and customize a system built with Akka.