265 lines
9.4 KiB
ReStructuredText
265 lines
9.4 KiB
ReStructuredText
.. _remoting-scala:
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#################
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Remoting (Scala)
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#################
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.. sidebar:: Contents
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.. contents:: :local:
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For an introduction of remoting capabilities of Akka please see :ref:`remoting`.
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Preparing your ActorSystem for Remoting
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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The Akka remoting is a separate jar file. Make sure that you have the following dependency in your project::
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"com.typesafe.akka" % "akka-remote" % "2.0-SNAPSHOT"
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To enable remote capabilities in your Akka project you should, at a minimum, add the following changes
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to your ``application.conf`` file::
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akka {
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actor {
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provider = "akka.remote.RemoteActorRefProvider"
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}
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remote {
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transport = "akka.remote.netty.NettyRemoteSupport"
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server {
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hostname = "127.0.0.1"
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port = 2552
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}
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}
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}
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As you can see in the example above there are four things you need to add to get started:
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* Change provider from ``akka.actor.LocalActorRefProvider`` to ``akka.remote.RemoteActorRefProvider``
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* Add host name - the machine you want to run the actor system on; this host
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name is exactly what is passed to remote systems in order to identify this
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system and consequently used for connecting back to this system if need be,
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hence set it to a reachable IP address or resolvable name in case you want to
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communicate across the network.
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* Add port number - the port the actor system should listen on, set to 0 to have it chosen automatically
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The example above only illustrates the bare minimum of properties you have to add to enable remoting.
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There are lots of more properties that are related to remoting in Akka. We refer to the following
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reference file for more information:
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.. literalinclude:: ../../akka-remote/src/main/resources/reference.conf
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:language: none
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Types of Remote Interaction
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^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Akka has two ways of using remoting:
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* Lookup : used to look up an actor on a remote node with ``actorFor(path)``
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* Creation : used to create an actor on a remote node with ``actorOf(Props(...), actorName)``
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In the next sections the two alternatives are described in detail.
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Looking up Remote Actors
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^^^^^^^^^^^^^^^^^^^^^^^^
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``actorFor(path)`` will obtain an ``ActorRef`` to an Actor on a remote node, e.g.::
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val actor = context.actorFor("akka://actorSystemName@10.0.0.1:2552/user/actorName")
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As you can see from the example above the following pattern is used to find an ``ActorRef`` on a remote node::
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akka://<actor system>@<hostname>:<port>/<actor path>
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Once you obtained a reference to the actor you can interact with it they same way you would with a local actor, e.g.::
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actor ! "Pretty awesome feature"
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For more details on how actor addresses and paths are formed and used, please refer to :ref:`addressing`.
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Creating Actors Remotely
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^^^^^^^^^^^^^^^^^^^^^^^^
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If you want to use the creation functionality in Akka remoting you have to further amend the
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``application.conf`` file in the following way (only showing deployment section)::
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akka {
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actor {
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deployment {
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/sampleActor {
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remote = "akka://sampleActorSystem@127.0.0.1:2553"
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}
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}
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}
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}
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The configuration above instructs Akka to react when an actor with path ``/sampleActor`` is created, i.e.
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using ``system.actorOf(Props(...)`, sampleActor)``. This specific actor will not be directly instantiated,
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but instead the remote daemon of the remote system will be asked to create the actor,
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which in this sample corresponds to ``sampleActorSystem@127.0.0.1:2553``.
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Once you have configured the properties above you would do the following in code::
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class SampleActor extends Actor { def receive = { case _ => println("Got something") } }
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val actor = context.actorOf(Props[SampleActor], "sampleActor")
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actor ! "Pretty slick"
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``SampleActor`` has to be available to the runtimes using it, i.e. the classloader of the
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actor systems has to have a JAR containing the class.
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Programmatic Remote Deployment
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------------------------------
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To allow dynamically deployed systems, it is also possible to include
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deployment configuration in the :class:`Props` which are used to create an
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actor: this information is the equivalent of a deployment section from the
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configuration file, and if both are given, the external configuration takes
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precedence.
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With these imports:
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.. includecode:: code/akka/docs/remoting/RemoteDeploymentDocSpec.scala#import
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and a remote address like this:
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.. includecode:: code/akka/docs/remoting/RemoteDeploymentDocSpec.scala#make-address
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you can advise the system to create a child on that remote node like so:
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.. includecode:: code/akka/docs/remoting/RemoteDeploymentDocSpec.scala#deploy
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Serialization
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^^^^^^^^^^^^^
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When using remoting for actors you must ensure that the ``props`` and ``messages`` used for
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those actors are serializable. Failing to do so will cause the system to behave in an unintended way.
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For more information please see :ref:`serialization-scala`
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Routers with Remote Destinations
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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It is absolutely feasible to combine remoting with :ref:`routing-scala`.
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This is also done via configuration::
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akka {
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actor {
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deployment {
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/serviceA/aggregation {
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router = "round-robin"
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nr-of-instances = 10
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target {
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nodes = ["akka://app@10.0.0.2:2552", "akka://app@10.0.0.3:2552"]
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}
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}
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}
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}
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}
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This configuration setting will clone the actor “aggregation” 10 times and deploy it evenly distributed across
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the two given target nodes.
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Description of the Remoting Sample
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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There is a more extensive remote example that comes with the Akka distribution.
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Please have a look here for more information: `Remote Sample
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<https://github.com/jboner/akka/tree/master/akka-samples/akka-sample-remote>`_
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This sample demonstrates both, remote deployment and look-up of remote actors.
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First, let us have a look at the common setup for both scenarios (this is
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``common.conf``):
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.. includecode:: ../../akka-samples/akka-sample-remote/src/main/resources/common.conf
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This enables the remoting by installing the :class:`RemoteActorRefProvider` and
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chooses the default remote transport. All other options will be set
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specifically for each show case.
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.. note::
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Be sure to replace the default IP 127.0.0.1 with the real address the system
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is reachable by if you deploy onto multiple machines!
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.. _remote-lookup-sample-scala:
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Remote Lookup
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-------------
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In order to look up a remote actor, that one must be created first. For this
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purpose, we configure an actor system to listen on port 2552 (this is a snippet
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from ``application.conf``):
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.. includecode:: ../../akka-samples/akka-sample-remote/src/main/resources/application.conf
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:include: calculator
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Then the actor must be created. For all code which follows, assume these imports:
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.. includecode:: ../../akka-samples/akka-sample-remote/src/main/scala/sample/remote/calculator/LookupApplication.scala
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:include: imports
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The actor doing the work will be this one:
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.. includecode:: ../../akka-samples/akka-sample-remote/src/main/scala/sample/remote/calculator/CalculatorApplication.scala
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:include: actor
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and we start it within an actor system using the above configuration
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.. includecode:: ../../akka-samples/akka-sample-remote/src/main/scala/sample/remote/calculator/CalculatorApplication.scala
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:include: setup
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With the service actor up and running, we may look it up from another actor
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system, which will be configured to use port 2553 (this is a snippet from
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``application.conf``).
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.. includecode:: ../../akka-samples/akka-sample-remote/src/main/resources/application.conf
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:include: remotelookup
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The actor which will query the calculator is a quite simple one for demonstration purposes
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.. includecode:: ../../akka-samples/akka-sample-remote/src/main/scala/sample/remote/calculator/LookupApplication.scala
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:include: actor
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and it is created from an actor system using the aforementioned client’s config.
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.. includecode:: ../../akka-samples/akka-sample-remote/src/main/scala/sample/remote/calculator/LookupApplication.scala
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:include: setup
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Requests which come in via ``doSomething`` will be sent to the client actor
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along with the reference which was looked up earlier. Observe how the actor
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system name using in ``actorFor`` matches the remote system’s name, as do IP
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and port number. Top-level actors are always created below the ``"/user"``
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guardian, which supervises them.
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Remote Deployment
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-----------------
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Creating remote actors instead of looking them up is not visible in the source
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code, only in the configuration file. This section is used in this scenario
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(this is a snippet from ``application.conf``):
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.. includecode:: ../../akka-samples/akka-sample-remote/src/main/resources/application.conf
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:include: remotecreation
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For all code which follows, assume these imports:
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.. includecode:: ../../akka-samples/akka-sample-remote/src/main/scala/sample/remote/calculator/LookupApplication.scala
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:include: imports
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The client actor looks like in the previous example
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.. includecode:: ../../akka-samples/akka-sample-remote/src/main/scala/sample/remote/calculator/CreationApplication.scala
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:include: actor
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but the setup uses only ``actorOf``:
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.. includecode:: ../../akka-samples/akka-sample-remote/src/main/scala/sample/remote/calculator/CreationApplication.scala
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:include: setup
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Observe how the name of the server actor matches the deployment given in the
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configuration file, which will transparently delegate the actor creation to the
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remote node.
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