# Akka — Resilient Distributed Actor Framework for the JVM

> Akka is a toolkit for building concurrent, distributed, and fault-tolerant applications on the JVM using the Actor Model. It provides tools for clustering, persistence, streaming, and HTTP services in Scala and Java.

## Install

Save as a script file and run:

# Akka — Resilient Distributed Actor Framework for the JVM

## Quick Use
```scala
// build.sbt
libraryDependencies += "com.typesafe.akka" %% "akka-actor-typed" % "2.10.+"

// Minimal typed actor
import akka.actor.typed.scaladsl.Behaviors
import akka.actor.typed.ActorSystem

val system = ActorSystem(Behaviors.receiveMessage[String] { msg =>
  println(s"Received: $msg"); Behaviors.same
}, "hello")
system ! "Hello Akka"
```

## Introduction
Akka is a JVM toolkit that implements the Actor Model to simplify building concurrent and distributed systems. Originally inspired by Erlang's process model, it provides a high-level abstraction for managing state, concurrency, and fault tolerance without manual thread management.

## What Akka Does
- Provides lightweight actors that encapsulate state and communicate via asynchronous messages
- Offers cluster membership, sharding, and distributed data for multi-node deployments
- Includes Akka Streams for backpressure-aware stream processing
- Supports event sourcing and CQRS through Akka Persistence
- Ships Akka HTTP for building RESTful and WebSocket services

## Architecture Overview
Akka runs on the JVM and uses a dispatcher-based execution model where actors share thread pools. Each actor has a mailbox for queued messages and processes them one at a time, eliminating the need for locks. The cluster module uses a gossip protocol for membership and failure detection. Akka Persistence uses event journals (Cassandra, JDBC, or others) to durably store actor state changes.

## Self-Hosting & Configuration
- Add Akka dependencies via sbt, Maven, or Gradle for Scala or Java projects
- Configure via application.conf using the HOCON format (Lightbend Config)
- Cluster settings define seed nodes, split-brain resolution, and down strategies
- Akka Persistence requires a journal and snapshot plugin (Cassandra, R2DBC, or JDBC)
- Logging integrates with SLF4J; default backend is Logback

## Key Features
- Supervision hierarchies automatically restart failed actors for self-healing systems
- Cluster Sharding distributes actors across nodes by entity ID
- Akka Streams implements the Reactive Streams specification with backpressure
- Location transparency: actors communicate the same way whether local or remote
- Akka Projections reads event journals for CQRS read-side processing

## Comparison with Similar Tools
- **Erlang/OTP** — the original actor model platform; Akka brings similar patterns to the JVM ecosystem
- **Orleans (Microsoft)** — virtual actor model for .NET; Akka offers more explicit lifecycle control
- **Vert.x** — event-driven toolkit for the JVM; Akka adds supervision trees and cluster sharding
- **Quarkus** — reactive Java framework; Akka provides a more opinionated actor-based concurrency model
- **Project Loom (Virtual Threads)** — lightweight threads in Java; Akka adds distribution, persistence, and fault tolerance on top

## FAQ
**Q: Is Akka free to use?**
A: Akka changed its license to the Business Source License (BSL 1.1) in 2022. It is free for small companies and non-production use; larger production deployments require a commercial license from Lightbend.

**Q: Can I use Akka with Java?**
A: Yes. Akka provides full Java APIs alongside Scala APIs for all modules.

**Q: What is the difference between Classic and Typed Akka?**
A: Typed Akka (akka-actor-typed) uses compile-time message type checking and is the recommended API. Classic Akka uses untyped ActorRef and is maintained for backward compatibility.

**Q: How does Akka handle node failures in a cluster?**
A: The cluster gossip protocol detects unreachable nodes. A configurable split-brain resolver decides whether to down unreachable members or keep them as candidates for recovery.

## Sources
- https://github.com/akka/akka
- https://akka.io/docs/

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Source: https://tokrepo.com/en/workflows/asset-c49078fe
Author: Script Depot