204 lines
8.6 KiB
Markdown
204 lines
8.6 KiB
Markdown
---
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project.description: Multi node testing of distributed systems built with Pekko.
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---
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# Multi Node Testing
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## Module info
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To use Multi Node Testing, you must add the following dependency in your project:
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@@dependency[sbt,Maven,Gradle] {
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bomGroup=org.apache.pekko bomArtifact=pekko-bom_$scala.binary.version$ bomVersionSymbols=PekkoVersion
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symbol1=PekkoVersion
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value1="$pekko.version$"
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group=org.apache.pekko
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artifact=pekko-multi-node-testkit_$scala.binary.version$
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version=PekkoVersion
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scope=test
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}
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@@project-info{ projectId="multi-node-testkit" }
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## Multi Node Testing Concepts
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When we talk about multi node testing in Pekko 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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* @ref:[The Test Conductor](#the-test-conductor). that coordinates and controls the nodes under test.
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* @ref:[The Multi Node Spec](#the-multi-node-spec). that is a convenience wrapper for starting the @apidoc[TestConductor$] and letting all
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nodes connect to it.
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* @ref:[The SbtMultiJvm Plugin](#the-sbtmultijvm-plugin). that starts tests in multiple JVMs possibly on multiple machines.
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## The Test Conductor
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The basis for the multi node testing is the @apidoc[TestConductor$]. It is a Pekko 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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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. More information on the
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possible operations is available in the @apidoc[remote.testconductor.Conductor](Conductor) API documentation.
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## The Multi Node Spec
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The Multi Node Spec consists of two parts. The @apidoc[MultiNodeConfig] that is responsible for common
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configuration and enumerating and naming the nodes under test. The `MultiNodeSpec` that contains a number
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of convenience functions for making the test nodes interact with each other. More information on the possible
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operations is available in the @apidoc[remote.testkit.MultiNodeSpec](MultiNodeSpec) API documentation.
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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 be set on the JVM command line with `-Dproperty=value`.
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These are the available properties:
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:
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*
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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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*
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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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*
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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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*
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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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*
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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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*
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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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The @ref:[SbtMultiJvm Plugin](multi-jvm-testing.md) 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 run multi node tests
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on a single machine without any special configuration by running them as normal multi-jvm tests. These tests can
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then be run distributed over multiple machines without any changes 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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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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@@@
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These are the available sbt multi-node settings:
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:
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*
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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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*
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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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*
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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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*
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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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:
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*
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`localhost`
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The current user on localhost using the default java.
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*
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`user1@host1`
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User `user1` on host `host1` with the default java.
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*
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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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*
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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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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 `multiNodeTest` task:
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```none
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multiNodeTest
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```
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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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```none
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multi-jvm:test
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```
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To run individual tests use the `multiNodeTestOnly` task:
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```none
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multiNodeTestOnly your.MultiNodeTest
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```
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To run individual tests in the multi-jvm mode do:
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```none
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multi-jvm:testOnly your.MultiNodeTest
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```
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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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## A Multi Node Testing Example
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First we need some scaffolding to hook up the @apidoc[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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@@snip [STMultiNodeSpec.scala](/remote-tests/src/test/scala/org/apache/pekko/remote/testkit/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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@@snip [MultiNodeSample.scala](/remote-tests/src/multi-jvm/scala/org/apache/pekko/remote/sample/MultiNodeSample.scala) { #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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@@snip [MultiNodeSample.scala](/remote-tests/src/multi-jvm/scala/org/apache/pekko/remote/sample/MultiNodeSample.scala) { #package #spec }
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## Things to Keep in Mind
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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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* To be able to use `blackhole`, `passThrough`, and `throttle` you must activate the failure injector and
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throttler transport adapters by specifying @scala[@scaladoc[testTransport(on = true)](pekko.remote.testkit.MultiNodeConfig#testTransport(on:Boolean):Unit)]@java[@javadoc[testTransport(true)](pekko.remote.testkit.MultiNodeConfig#testTransport(boolean))] in your `MultiNodeConfig`.
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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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## Configuration
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There are several configuration properties for the Multi-Node Testing module, please refer
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to the @ref:[reference configuration](general/configuration-reference.md#config-pekko-multi-node-testkit).
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