Akka

Akka is a toolkit and runtime for building highly concurrent, distributed, and fault-tolerant applications on the Java Virtual Machine (JVM) and, via ports and bindings, on other platforms such as .NET (Akka.NET). At its core it implements the actor model: actors encapsulate state and behavior, communicate exclusively through asynchronous messages, process messages one at a time, and can create child actors. Supervisors monitor failures and can restart or substitute actors, enabling resilience without shared mutable state.

An Akka application runs inside an actor system. Messages are sent to actors and handled by their mailboxes, with dispatchers controlling concurrency. Features include location transparency through clustering and remoting, which lets actors span multiple machines, and a supervision strategy for fault tolerance.

The ecosystem includes two API styles: Classic and Typed. Akka Typed offers a more type-safe interface for defining message protocols. Core modules cover Akka Cluster (distributed actors), Akka Persistence (durable state with journal and snapshots), Akka Sharding (distributing actors across a cluster), Akka Streams (reactive streams integration), and Akka HTTP (HTTP server). Additional projects provide integration with other technologies and domains within the Akka ecosystem.

Use cases include scalable backends, real-time processing, and microservices architectures. Akka originated in the Scala and Java ecosystem, with Jonas Bonér introducing the project in 2009; it is maintained by Lightbend and the community, and remains a prominent option for building resilient, asynchronous systems.