2013-11-26 09:17:50 +01:00
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<title>Akka Remote Samples with Java</title>
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<body>
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<div>
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<p>
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2014-03-07 13:43:05 +01:00
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In order to showcase the <a href="http://doc.akka.io/docs/akka/2.4-SNAPSHOT/java/remoting.html" target="_blank">remote capabilities of Akka</a>
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2013-11-26 09:17:50 +01:00
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we thought a remote calculator could do the trick.
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This sample demonstrates both remote deployment and look-up of remote actors.
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</div>
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<div>
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<h2>Lookup Remote Actors</h2>
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<p>
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This sample involves two actor systems.
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<ul>
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<li><b>CalculatorSystem</b> listens on port 2552 and starts one actor, the
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<a href="#code/src/main/java/sample/remote/calculator/CalculatorActor.java" class="shortcut">CalculatorActor</a>
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that provides a service for arithmetic operations.</li>
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<li><b>LookupSystem</b> listens on port 2553 and starts one actor, the
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<a href="#code/src/main/java/sample/remote/calculator/LookupActor.java" class="shortcut">LookupActor</a>
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that sends operations to the remote calculator service.</li>
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</ul>
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<p>
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Open <a href="#code/src/main/java/sample/remote/calculator/LookupApplication.java" class="shortcut">LookupApplication.java</a>.
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</p>
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<p>
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There you see how the two actor systems and actors are started. In this first step they are running in the same JVM process,
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but you can run them in separate processes as described later. Note that this changes nothing in the configuration or implementation.
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</p>
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<p>
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The two actor systems use different configuration, which is where the listen port is defined.
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The CalculatorSystem uses <a href="#code/src/main/resources/calculator.conf" class="shortcut">calculator.conf</a>
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and the LookupSystem uses <a href="#code/src/main/resources/remotelookup.conf" class="shortcut">remotelookup.conf</a>.
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</p>
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<p>
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Note that the configuration files also import the
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<a href="#code/src/main/resources/common.conf" class="shortcut">common.conf</a>.
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This enables the remoting by installing the RemoteActorRefProvider and chooses the default remote transport.
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Be sure to replace the default IP 127.0.0.1 with the real address the system is reachable
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by if you deploy onto multiple machines!
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</p>
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<p>
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The <a href="#code/src/main/java/sample/remote/calculator/CalculatorActor.java" class="shortcut">CalculatorActor</a>
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does not illustrate anything exciting. More interesting is the
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<a href="#code/src/main/java/sample/remote/calculator/LookupActor.java" class="shortcut">LookupActor</a>.
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It takes a String <code>path</code> as constructor parameter. This is the full path, including the remote
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address of the calculator service. Observe how the actor system name of the path matches the remote system’s
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name, as do IP and port number. Top-level actors are always created below the "/user" guardian, which supervises them.
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</p>
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<pre><code>
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"akka.tcp://CalculatorSystem@127.0.0.1:2552/user/calculator"
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</code></pre>
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<p>
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First it sends an <code>Identify</code> message to the actor selection of the path.
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The remote calculator actor will reply with <code>ActorIdentity</code> containing its <code>ActorRef</code>.
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<code>Identify</code> is a built-in message that all Actors will understand and automatically reply to with a
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<code>ActorIdentity</code>. If the identification fails it will be retried after the scheduled timeout
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by the <code>LookupActor</code>.
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</p>
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<p>
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Note how none of the code is specific to remoting, this also applies when talking to a local actor which
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might terminate and be recreated. That is what we call Location Transparency.
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</p>
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<p>
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Once it has the <code>ActorRef</code> of the remote service it can <code>watch</code> it. The remote system
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might be shutdown and later started up again, then <code>Terminated</code> is received on the watching
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side and it can retry the identification to establish a connection to the new remote system.
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</p>
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</div>
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<div>
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<h2>Run the Lookup Sample</h2>
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<p>
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To run this sample, go to the <a href="#run" class="shortcut">Run</a>
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tab, and start the application main class <code>sample.remote.calculator.LookupApplication</code> if it is not already started.
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</p>
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<p>
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In the log pane you should see something like:
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</p>
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<pre><code>
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Started LookupSystem
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Calculating 74 - 42
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Sub result: 74 - 42 = 32
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Calculating 15 + 71
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Add result: 15 + 71 = 86
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</code></pre>
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<p>
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The two actor systems are running in the same JVM process. It can be more interesting to run them in separate
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processes. Stop the application in the <a href="#run" class="shortcut">Run</a> tab and then open two
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terminal windows.
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</p>
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<p>
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Start the CalculatorSystem in the first terminal window with the following command (on one line):
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</p>
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<pre><code>
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<path to activator dir>/activator
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"run-main sample.remote.calculator.LookupApplication Calculator"
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</code></pre>
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<p>
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Start the LookupSystem in the second terminal window with the following command (on one line):
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</p>
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<pre><code>
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<path to activator dir>/activator
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"run-main sample.remote.calculator.LookupApplication Lookup"
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</code></pre>
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<p>
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Thereafter you can try to shutdown the CalculatorSystem in the first terminal window with
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'ctrl-c' and then start it again. In the second terminal window you should see the
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failure detection and then how the successful calculation results are logged again when it has
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established a connection to the new system.
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</p>
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</div>
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<div>
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<h2>Create Remote Actors</h2>
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<p>
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This sample involves two actor systems.
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</p>
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<ul>
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<li><b>CalculatorWorkerSystem</b> listens on port 2552</li>
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<li><b>CreationSystem</b> listens on port 2554 and starts one actor, the
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<a href="#code/src/main/java/sample/remote/calculator/CreationActor.java" class="shortcut">CreationActor</a>
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that creates remote calculator worker actors in the CalculatorWorkerSystem and sends operations to them.</li>
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</ul>
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<p>
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Open <a href="#code/src/main/java/sample/remote/calculator/CreationApplication.java" class="shortcut">CreationApplication.java</a>.
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</p>
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<p>
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There you see how the two actor systems and actors are started. In this first step they are running in the same JVM process,
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but you can run them in separate processes as described later.
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</p>
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<p>
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The two actor systems use different configuration, which is where the listen port is defined.
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The CalculatorWorkerSystem uses <a href="#code/src/main/resources/calculator.conf" class="shortcut">calculator.conf</a>
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and the CreationSystem uses <a href="#code/src/main/resources/remotecreation.conf" class="shortcut">remotecreation.conf</a>.
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</p>
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<p>
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Note that the configuration files also import the
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<a href="#code/src/main/resources/common.conf" class="shortcut">common.conf</a>.
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This enables the remoting by installing the RemoteActorRefProvider and chooses the default remote transport.
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Be sure to replace the default IP 127.0.0.1 with the real address the system is reachable
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by if you deploy onto multiple machines!
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</p>
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<p>
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The <a href="#code/src/main/java/sample/remote/calculator/CreationActor.java" class="shortcut">CreationActor</a>
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creates a child <a href="#code/src/main/java/sample/remote/calculator/CalculatorActor.java" class="shortcut">CalculatorActor</a>
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for each incoming <code>MathOp</code> message. The
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<a href="#code/src/main/resources/remotecreation.conf" class="shortcut">configuration</a> contains a deployment section that
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matches these child actors and defines that the actors are to be deployed at the remote system. The wildcard (*) is needed
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because the child actors are created with unique anonymous names.
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</p>
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<pre><code>
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akka.actor.deployment {
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/creationActor/* {
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remote = "akka.tcp://CalculatorWorkerSystem@127.0.0.1:2552"
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}
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}
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</code></pre>
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<p>
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Error handling, i.e. supervision, works exactly in the same way as if the child actor was a local child actor.
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In addtion, in case of network failures or JVM crash the child will be terminated and automatically removed
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from the parent even though they are located on different machines.
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</p>
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</div>
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<div>
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<h2>Run the Creation Sample</h2>
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<p>
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To run this sample, go to the <a href="#run" class="shortcut">Run</a>
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tab, and start the application main class <code>sample.remote.calculator.CreationApplication</code> if it is not already started.
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</p>
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<p>
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In the log pane you should see something like:
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</p>
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<pre><code>
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Started CreationSystem
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Calculating 7135 / 62
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Div result: 7135 / 62 = 115.08
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Calculating 0 * 9
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Mul result: 0 * 9 = 0
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</code></pre>
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<p>
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The two actor systems are running in the same JVM process. It can be more interesting to run them in separate
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processes. Stop the application in the <a href="#run" class="shortcut">Run</a> tab and then open two
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terminal windows.
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</p>
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<p>
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Start the CalculatorWorkerSystem in the first terminal window with the following command (on one line):
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</p>
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<pre><code>
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<path to activator dir>/activator
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"run-main sample.remote.calculator.CreationApplication CalculatorWorker"
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</code></pre>
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<p>
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Start the CreationSystem in the second terminal window with the following command (on one line):
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</p>
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<pre><code>
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<path to activator dir>/activator
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"run-main sample.remote.calculator.CreationApplication Creation"
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</code></pre>
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<p>
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Thereafter you can try to shutdown the CalculatorWorkerSystem in the first terminal window with
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'ctrl-c' and then start it again. In the second terminal window you should see the
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failure detection and then how the successful calculation results are logged again when it has
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established a connection to the new system.
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</p>
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</div>
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</body>
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</html>
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