.. _remoting-java: ##################### Remoting (Java) ##################### For an introduction of remoting capabilities of Akka please see :ref:`remoting`. Preparing your ActorSystem for Remoting ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ The Akka remoting is a separate jar file. Make sure that you have the following dependency in your project:: com.typesafe.akka akka-remote 2.0-SNAPSHOT To enable remote capabilities in your Akka project you should, at a minimum, add the following changes to your ``application.conf`` file:: akka { actor { provider = "akka.remote.RemoteActorRefProvider" } remote { transport = "akka.remote.netty.NettyRemoteTransport" server { hostname = "127.0.0.1" port = 2552 } } } As you can see in the example above there are four things you need to add to get started: * Change provider from ``akka.actor.LocalActorRefProvider`` to ``akka.remote.RemoteActorRefProvider`` * Add host name - the machine you want to run the actor system on; this host name is exactly what is passed to remote systems in order to identify this system and consequently used for connecting back to this system if need be, hence set it to a reachable IP address or resolvable name in case you want to communicate across the network. * Add port number - the port the actor system should listen on, set to 0 to have it chosen automatically The example above only illustrates the bare minimum of properties you have to add to enable remoting. There are lots of more properties that are related to remoting in Akka. We refer to the following reference file for more information: .. literalinclude:: ../../akka-remote/src/main/resources/reference.conf :language: none Looking up Remote Actors ^^^^^^^^^^^^^^^^^^^^^^^^ ``actorFor(path)`` will obtain an ``ActorRef`` to an Actor on a remote node:: ActorRef actor = context.actorFor("akka://app@10.0.0.1:2552/user/serviceA/retrieval"); As you can see from the example above the following pattern is used to find an ``ActorRef`` on a remote node:: akka://@:/ For more details on how actor addresses and paths are formed and used, please refer to :ref:`addressing`. Creating Actors Remotely ^^^^^^^^^^^^^^^^^^^^^^^^ The configuration below instructs the system to deploy the actor "retrieval” on the specific host "app@10.0.0.1". The "app" in this case refers to the name of the ``ActorSystem`` (only showing deployment section):: akka { actor { deployment { /serviceA/retrieval { remote = "akka://app@10.0.0.1:2552" } } } } Logical path lookup is supported on the node you are on, i.e. to use the actor created above you would do the following: .. includecode:: code/akka/docs/remoting/RemoteActorExample.java#localNodeActor This will obtain an ``ActorRef`` on a remote node: .. includecode:: code/akka/docs/remoting/RemoteActorExample.java#remoteNodeActor As you can see from the example above the following pattern is used to find an ``ActorRef`` on a remote node:: akka://@:/ Programmatic Remote Deployment ------------------------------ To allow dynamically deployed systems, it is also possible to include deployment configuration in the :class:`Props` which are used to create an actor: this information is the equivalent of a deployment section from the configuration file, and if both are given, the external configuration takes precedence. With these imports: .. includecode:: code/akka/docs/remoting/RemoteDeploymentDocTestBase.java#import and a remote address like this: .. includecode:: code/akka/docs/remoting/RemoteDeploymentDocTestBase.java#make-address you can advise the system to create a child on that remote node like so: .. includecode:: code/akka/docs/remoting/RemoteDeploymentDocTestBase.java#deploy Serialization ^^^^^^^^^^^^^ When using remoting for actors you must ensure that the ``props`` and ``messages`` used for those actors are serializable. Failing to do so will cause the system to behave in an unintended way. For more information please see :ref:`serialization-java` Routers with Remote Destinations ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ It is absolutely feasible to combine remoting with :ref:`routing-java`. This is also done via configuration:: akka { actor { deployment { /serviceA/aggregation { router = "round-robin" nr-of-instances = 10 target { nodes = ["akka://app@10.0.0.2:2552", "akka://app@10.0.0.3:2552"] } } } } } This configuration setting will clone the actor “aggregation” 10 times and deploy it evenly distributed across the two given target nodes. Description of the Remoting Sample ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ There is a more extensive remote example that comes with the Akka distribution. Please have a look here for more information: `Remote Sample `_ This sample demonstrates both, remote deployment and look-up of remote actors. First, let us have a look at the common setup for both scenarios (this is ``common.conf``): .. includecode:: ../../akka-samples/akka-sample-remote/src/main/resources/common.conf This enables the remoting by installing the :class:`RemoteActorRefProvider` and chooses the default remote transport. All other options will be set specifically for each show case. .. note:: Be sure to replace the default IP 127.0.0.1 with the real address the system is reachable by if you deploy onto multiple machines! .. _remote-lookup-sample-java: Remote Lookup ------------- In order to look up a remote actor, that one must be created first. For this purpose, we configure an actor system to listen on port 2552 (this is a snippet from ``application.conf``): .. includecode:: ../../akka-samples/akka-sample-remote/src/main/resources/application.conf :include: calculator Then the actor must be created. For all code which follows, assume these imports: .. includecode:: ../../akka-samples/akka-sample-remote/src/main/java/sample/remote/calculator/java/JLookupApplication.java :include: imports The actor doing the work will be this one: .. includecode:: ../../akka-samples/akka-sample-remote/src/main/java/sample/remote/calculator/java/JSimpleCalculatorActor.java :include: actor and we start it within an actor system using the above configuration .. includecode:: ../../akka-samples/akka-sample-remote/src/main/java/sample/remote/calculator/java/JCalculatorApplication.java :include: setup With the service actor up and running, we may look it up from another actor system, which will be configured to use port 2553 (this is a snippet from ``application.conf``). .. includecode:: ../../akka-samples/akka-sample-remote/src/main/resources/application.conf :include: remotelookup The actor which will query the calculator is a quite simple one for demonstration purposes .. includecode:: ../../akka-samples/akka-sample-remote/src/main/java/sample/remote/calculator/java/JLookupActor.java :include: actor and it is created from an actor system using the aforementioned client’s config. .. includecode:: ../../akka-samples/akka-sample-remote/src/main/java/sample/remote/calculator/java/JLookupApplication.java :include: setup Requests which come in via ``doSomething`` will be sent to the client actor along with the reference which was looked up earlier. Observe how the actor system name using in ``actorFor`` matches the remote system’s name, as do IP and port number. Top-level actors are always created below the ``"/user"`` guardian, which supervises them. Remote Deployment ----------------- Creating remote actors instead of looking them up is not visible in the source code, only in the configuration file. This section is used in this scenario (this is a snippet from ``application.conf``): .. includecode:: ../../akka-samples/akka-sample-remote/src/main/resources/application.conf :include: remotecreation For all code which follows, assume these imports: .. includecode:: ../../akka-samples/akka-sample-remote/src/main/java/sample/remote/calculator/java/JLookupApplication.java :include: imports The server actor can multiply or divide numbers: .. includecode:: ../../akka-samples/akka-sample-remote/src/main/java/sample/remote/calculator/java/JAdvancedCalculatorActor.java :include: actor The client actor looks like in the previous example .. includecode:: ../../akka-samples/akka-sample-remote/src/main/java/sample/remote/calculator/java/JCreationActor.java :include: actor but the setup uses only ``actorOf``: .. includecode:: ../../akka-samples/akka-sample-remote/src/main/java/sample/remote/calculator/java/JCreationApplication.java :include: setup Observe how the name of the server actor matches the deployment given in the configuration file, which will transparently delegate the actor creation to the remote node.