Effective Akka

Chapter 1. Actor Application Types

One of the questions I encounter the most when speaking at conferences is, “What is a use case for an Actor-based application?” That depends on what you’re trying to accomplish, but if you want to build an application that can manage concurrency, scale outwardly across nodes, and be fault tolerant, actors are a good fit for this role.

Domain-driven

In a domain-driven actor application, actors live and die to represent the state of the world in a live cache, where the mere existence of these actors and their encapsulation of state show the data for your application. They are frequently used in systems where information is provisioned to multiple other servers, which happens in an eventual consistency fashion. This implies that it is plausible that an actor attempting to supply another server may not be able to do so at a given point, and therefore must try until it can.

For example, imagine a large financial institution trying to keep a real-time view of all of its customers, with all of their accounts and all of the investments that customer owns via each account at a given time. This information can be created and maintained live through actor-supervisor hierarchies.

This kind of real-time domain modeling, where you are in essence creating a cache that also contains behavior, is enabled by the lightweight nature of Akka actors. Because Akka actors share resources (such as threads), each instance only takes about 400 bytes of heap space before you ...