Akka (toolkit)

Distinguishing features

The key points distinguishing applications based on Akka actors are:

• Concurrency is message-based and asynchronous: typically no mutable data are shared and no synchronization primitives are used; Akka implements the actor model.
• The way actors interact is the same whether they are on the same host or separate hosts, communicating directly or through routing facilities, running on a few threads or many threads, etc. Such details may be altered at deployment time through a configuration mechanism, allowing a program to be scaled up (to make use of more powerful servers) and out (to make use of more servers) without modification.
• Actors are arranged hierarchically with regard to program failures, which are treated as events to be handled by an actor's supervisor (regardless of which actor sent the message triggering the failure). In contrast to Erlang, Akka enforces parental supervision, which means that each actor is created and supervised by its parent actor.

Akka has a modular structure, with a core module providing actors. Other modules are available to add features such as network distribution of actors, cluster support, Command and Event Sourcing, integration with various third-party systems (e.g. Apache Camel, ZeroMQ), and even support for other concurrency models such as Futures and Agents.

Project structure

Viktor Klang became the technical lead for the Akka project in September 2011. When Viktor became Director of Engineering at Lightbend in December 2012, Roland Kuhn became the technical lead for Akka. The main part of the development is done by a core team employed at Lightbend, supported by an active community. The current emphasis is on extending cluster support.

Relation to other libraries

Other frameworks and toolkits have emerged to form an ecosystem around Akka:

• The Spray toolkit is implemented using Akka and features a HTTP server as well as related facilities, such as a domain-specific language (DSL) for creating RESTful APIs
• The Play framework for developing web applications offers integration with Akka
• Up until version 1.6, Apache Spark used Akka for communication between nodes
• The Socko Web Server library supports the implementation of REST APIs for Akka applications
• The eventsourced library provides event-driven architecture (see also domain-driven design) support for Akka actors
• The Gatling stress test tool for load-testing web servers is built upon Akka
• The Scalatra web framework offers integration with Akka.
• The Vaadin web app development framework can integrate with Akka
• The Apache Flink (platform for distributed stream and batch data processing) RPC system is built using Akka but isolated since v1.14.
• The Lagom framework for building reactive microservices is implemented on top of Akka.

There are more than 250 public projects registered on GitHub which use Akka.

Publications about Akka

There are several books about Akka:

• Akka Essentials
• Akka Code Examples
• Akka Concurrency
• Akka in Action, Second Edition
• Akka in Action
• Effective Akka
• Composable Futures with Akka 2.0, Featuring Java, Scala and Akka Code Examples

Akka also features in:

• P. Haller's "Actors in Scala"
• N. Raychaudhuri's "Scala in Action"
• D. Wampler's "Functional Programming for Java Developers"
• A. Alexander's "Scala Cookbook"
• V. Subramaniam's "Programming Concurrency on the JVM"
• M. Bernhardt's "Reactive Web Applications"

Besides many web articles that describe the commercial use of Akka, there are also overview articles about it.