Cleanup after merge.
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Björn Antonsson
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.. _multi-node-testing:
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###################
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Multi Node Testing
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###################
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.. note:: This module is :ref:`experimental <experimental>`. This document describes how to use the features
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implemented so far. More features are coming in Akka Coltrane. Track progress of the Coltrane milestone in
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`Assembla <http://www.assembla.com/spaces/akka/milestones/418132-coltrane>`_.
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Multi Node Testing Concepts
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===========================
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When we talk about multi node testing in Akka we mean the process of running coordinated tests on multiple actor
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systems in different JVMs. The multi node testing kit consist of three main parts.
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* `The Test Conductor`_. that coordinates and controls the nodes under test.
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* `The Multi Node Spec`_. that is a convenience wrapper for starting the ``TestConductor`` and letting all
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nodes connect to it.
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* `The SbtMultiJvm Plugin`_. that starts tests in multiple JVMs possibly on multiple machines.
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The Test Conductor
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==================
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The basis for the multi node testing is the ``TestConductor``. It is an Akka Extension that plugs in to the
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network stack and it is used to coordinate the nodes participating in the test and provides several features
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including:
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* Node Address Lookup: Finding out the full path to another test node (No need to share configuration between
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test nodes)
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* Node Barrier Coordination: Waiting for other nodes at named barriers.
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* Network Failure Injection: Throttling traffic, dropping packets, unplugging and plugging nodes back in.
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This is a schematic overview of the test conductor.
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.. image:: ../images/akka-remote-testconductor.png
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The test conductor server is responsible for coordinating barriers and sending commands to the test conductor
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clients that act upon them, e.g. throttling network traffic to/from another client.
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The Multi Node Spec
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===================
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The Multi Node Spec consists of two parts. The ``MultiNodeConfig`` that is responsible for common
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configuration and enumerating and naming the nodes under test. The ``MultiNodeSpec`` that contains all the
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convenience functions for making the test nodes interact with each other.
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The setup of the ``MultiNodeSpec`` is configured through java system properties that you set on all JVMs that's going to run a
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node under test. These can easily be set on the JVM command line with ``-Dproperty=value``.
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These are the available properties:
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* ``multinode.max-nodes``
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The maximum number of nodes that a test can have.
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* ``multinode.host``
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The host name or IP for this node. Must be resolvable using InetAddress.getByName.
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* ``multinode.port``
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The port number for this node. Defaults to 0 which will use a random port.
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* ``multinode.server-host``
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The host name or IP for the server node. Must be resolvable using InetAddress.getByName.
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* ``multinode.server-port``
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The port number for the server node. Defaults to 4711.
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* ``multinode.index``
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The index of this node in the sequence of roles defined for the test. The index 0 is special and that machine
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will be the server. All failure injection and throttling must be done from this node.
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The SbtMultiJvm Plugin
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======================
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The :ref:`SbtMultiJvm Plugin <multi-jvm-testing>` has been updated to be able to run multi node tests, by
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automatically generating the relevant ``multinode.*`` properties. This means that you can easily run multi node tests
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on a single machine without any special configuration by just running them as normal multi-jvm tests. These tests can
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then be run distributed over multiple machines without any changes simply by using the multi-node additions to the
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plugin.
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Multi Node Specific Additions
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+++++++++++++++++++++++++++++
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The plugin also has a number of new ``multi-node-*`` sbt tasks and settings to support running tests on multiple
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machines. The necessary test classes and dependencies are packaged for distribution to other machines with
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`SbtAssembly <https://github.com/sbt/sbt-assembly>`_ into a jar file with a name on the format
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``<projectName>_<scalaVersion>-<projectVersion>-multi-jvm-assembly.jar``
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.. note::
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To be able to distribute and kick off the tests on multiple machines, it is assumed that both host and target
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systems are POSIX like systems with ``ssh`` and ``rsync`` available.
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These are the available sbt multi-node settings:
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* ``multiNodeHosts``
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A sequence of hosts to use for running the test, on the form ``user@host:java`` where host is the only required
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part. Will override settings from file.
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* ``multiNodeHostsFileName``
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A file to use for reading in the hosts to use for running the test. One per line on the same format as above.
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Defaults to ``multi-node-test.hosts`` in the base project directory.
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* ``multiNodeTargetDirName``
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A name for the directory on the target machine, where to copy the jar file. Defaults to ``multi-node-test`` in
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the base directory of the ssh user used to rsync the jar file.
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* ``multiNodeJavaName``
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The name of the default Java executable on the target machines. Defaults to ``java``.
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Here are some examples of how you define hosts:
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* ``localhost``
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The current user on localhost using the default java.
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* ``user1@host1``
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User ``user1`` on host ``host1`` with the default java.
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* ``user2@host2:/usr/lib/jvm/java-7-openjdk-amd64/bin/java``
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User ``user2`` on host ``host2`` using java 7.
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* ``host3:/usr/lib/jvm/java-6-openjdk-amd64/bin/java``
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The current user on host ``host3`` using java 6.
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Running the Multi Node Tests
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++++++++++++++++++++++++++++
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To run all the multi node test in multi-node mode (i.e. distributing the jar files and kicking off the tests
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remotely) from inside sbt, use the ``multi-node-test`` task:
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.. code-block:: none
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multi-node-test
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To run all of them in multi-jvm mode (i.e. all JVMs on the local machine) do:
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.. code-block:: none
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multi-jvm:test
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To run individual tests use the ``multi-node-test-only`` task:
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.. code-block:: none
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multi-node-test-only your.MultiNodeTest
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To run individual tests in the multi-jvm mode do:
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.. code-block:: none
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multi-jvm:test-only your.MultiNodeTest
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More than one test name can be listed to run multiple specific tests. Tab completion in sbt makes it easy to
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complete the test names.
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Preparing Your Project for Multi Node Testing
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=============================================
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The multi node testing kit is a separate jar file. Make sure that you have the following dependency in your project:
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.. parsed-literal::
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"com.typesafe.akka" %% "akka-remote-tests-experimental" % "2.1-SNAPSHOT" cross CrossVersion.full
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If you are using the latest nightly build you should pick a timestamped Akka version from
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`<http://repo.typesafe.com/typesafe/snapshots/com/typesafe/akka/>`_. Don't use ``SNAPSHOT``. Note that the
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Scala version |scalaVersion| is part of the artifactId.
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A Multi Node Testing Example
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============================
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First we need some scaffolding to hook up the ``MultiNodeSpec`` with your favorite test framework. Lets define a trait
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``STMultiNodeSpec`` that uses ScalaTest to start and stop ``MultiNodeSpec``.
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.. includecode:: ../../akka-samples/akka-sample-multi-node/src/test/scala/sample/multinode/STMultiNodeSpec.scala#example
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Then we need to define a configuration. Lets use two nodes ``"node1`` and ``"node2"`` and call it
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``MultiNodeSampleConfig``.
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.. includecode:: ../../akka-samples/akka-sample-multi-node/src/multi-jvm/scala/sample/multinode/MultiNodeSample.scala
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:include: package,config
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And then finally to the node test code. That starts the two nodes, and demonstrates a barrier, and a remote actor
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message send/receive.
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.. includecode:: ../../akka-samples/akka-sample-multi-node/src/multi-jvm/scala/sample/multinode/MultiNodeSample.scala
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:include: package,spec
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Things to Keep in Mind
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======================
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There are a couple of things to keep in mind when writing multi node tests or else your tests might behave in
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surprising ways.
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* Don't issue a shutdown of the first node. The first node is the controller and if it shuts down your test will break.
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* Throttling, shutdown and other failure injections can only be done from the first node, which again is the controller.
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* Don't ask for the address of a node using ``node(address)`` after the node has been shut down. Grab the address before
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shutting down the node.
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* Don't use MultiNodeSpec methods like address lookup, barrier entry et.c. from other threads than the main test
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thread. This also means that you shouldn't use them from inside an actor, a future, or a scheduled task.
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