Akka-Inspection

Akka-Inspection is an extension for Akka that can be used to expose an actor's state and make it inspectable from outside the cluster.

The extension comes in two flavors: a trait specific for actors using mutation as a way to transform their state and another one for actors that mutate their state by recursively calling context.become(...).

Mutable actor inspection

To add the ability to inspect a "mutable" actor the trait MutableInspection has to be mixed into the Actor.

This requires to implement fragments which can be seen as a set of getters on the actors state. See the section FragmentId and Fragment for more details.

val fragments: Map[FragmentId, Fragment]

Automatic derivation

fragments can be implemented automatically by using the helper function fragmentsFrom. See Inspectable for more details.

import akka.actor.Actor
import com.swissborg.akkainspection.MutableInspection
import com.swissborg.akkainspection.inspectable.Inspectable
import com.swissborg.akkainspection.inspectable.derivation.semiauto._

class MyMutableActor extends Actor with MutableInspection {
  import MyMutableActor._
  
  var s: State = ???
  
  override def receive  = ???
  
  override val fragments: Map[FragmentId, Fragment] = fragmentsFrom(s)
}

object MyMutableActor {
  case class State(/*...*/)
  object State {
    implicit val stateInspectable: Inspectable[State] = deriveInspectable
  }
}

Immutable actor inspection

To add the ability to inspect a "immutable" actor the trait ImmutableInspection has to be mixed into the Actor.

The trait exposes two methods: inspect and withInspection. These methods are used to enhance the existing Receive methods to be able to inspect the state. They do the same thing and choosing one over another is a matter of taste.

inspect can be used in an ... orElse ... pattern whereas withInspection wraps around an existing Receive.

The argument state in inspect or withInspection can be used to give a name to the current state in which the actor is. This will be visible when inspecting the actor.

FragmentId and Fragment

A Fragment represents a part of an actor's state. Such a fragment can be anything that can be extracted from the state. A FragmentId is then a way to access this fragment. It's simply a type-safe wrapper around a string.

Different types of Fragments exits:

Const

Const[T: Render](t: T) is a fragment that always returns the state-fragment t.

Always

Always[T: Render](t: => T) is a fragment that always returns the same state-fragment t. It differs to Const as it is pass by-name.

Getter

Getter[S, T: Render](get: S => T) is a fragment that extract a T from the state S.

Sensitive

A fragment that be used as a placeholder for sensitive data that should not be exposed to the outside.

Render

Render[A] is a typeclass used to render A (transform into a String). By default it uses toString but can be overidden by adding an instance in scope.

Inspectable

Inspectable[A] is a typeclass for As that are inspectable. In other words, where A can deconstructed into at least one Fragment.

Derivation

An instance can automatically derived for As that case classes or tuples. More generally, product types.

object Foo {
  case class A(l: List[Double])
  case class B(s: String, bar: innerB)
  case class innerB(i: Int)
  
  case class State(a: A, b: B)
}

The Inspectable instance for State will derive the most precise Fragments. The equivalent instance implemented by hand is:

val stateInspectable: Inspectable[State] = new Inspectable[State] {
  override val fragments: Map[FragmentId, inspection.Fragment[State]] = Map(
    FragmentId("a.l") -> Fragment.getter(_.a.l),
    FragmentId("b.s") -> Fragment.getter(_.b.s),
    FragmentId("b.bar.i") -> Fragment.getter(_.b.bar.i)
  )
}

Semi-automatic derivation

import com.swissborg.akkainspection.inspectable.Inspectable
import com.swissborg.akkainspection.inspectable.derivation.semiauto._

object Foo {
  case class A(l: List[Double])
  case class B(s: String, bar: innerB)
  case class innerB(i: Int)
  
  case class State(a: A, b: B)
  object State {
    val stateInspectable: Inspectable[State] = deriveInspectable
  }
}

Automatic derivation

Add the import com.swissborg.swissborg.akkainspection.inspectable.derivation.auto._ to derive an Inspectable without any boilerplate.