Akka Primer

1. The Actor Model

Actors are lightweight isolated units of computation that communicate exclusively via asynchronous messages. Each actor owns its mutable state, processes one message at a time, and never shares memory directly with another actor. This eliminates entire categories of concurrency bugs by construction.

2. Defining a Behavior

Akka Typed asks you to describe an actor as a Behavior. The example below shows a simple ping-pong responder that replies with a counter on every message received.

object Pinger {
  sealed trait Cmd
  case class Ping(replyTo: ActorRef[Pong]) extends Cmd
  case class Pong(count: Int)

  def apply(n: Int = 0): Behavior[Cmd] =
    Behaviors.receive { (ctx, msg) =>
      msg match {
        case Ping(reply) =>
          reply ! Pong(n + 1)
          apply(n + 1)
      }
    }
}

3. Supervision and Failure

Let it crash. Akka actors are supervised by their parent, and the parent decides whether to restart, resume, or stop a failing child. Combine this with persistence and clustering and you get systems that self-heal under load instead of collapsing into deadlock.