Mastering Functional Programming

Messaging guarantees

Akka is built to be deployed in clusters, over the network. This means that you have fewer delivery guarantees about the messages than when you are working on a single JVM application. If you are sending a message from an actor that resides in one computer to an actor on another side of the world, you cannot guarantee that this message will get delivered.

So, the actor model as implemented by Akka requires you to build your applications with no guarantees whatsoever about delivering the messages. Your application must be robust to the situations of the impossibility of message-delivery.

However, Akka provides you with a guarantee about the order in which messages from one actor to another get delivered. This means that ...