Setting up a testing cluster using ClusterRunner


So you have written some tests for your project and now you are waiting for the test run to be completed to see if anything breaks due to the changes you have made by your last commit. Finally you can merge your changes to develop when everything seems green on your CI. But when the number of tests increases, their execution time will also increase. Our problem was exactly that. It took more than ten hours to execute one of our testing suites. Since this was notable time duration, we needed a way to distribute tests across multiple VMs as our tests cannot be run in parallel in the same VM. Our CI system Bamboo has built in support for doing such a task by using Bamboo Remote Agents. But these remote agents do not come for free and whenever our tests get increased, we will have to purchase more and more agents. So we wanted to see if there are any existing solutions for this job and my client came up with this excellent open source tool called ClusterRunner. ClusterRunner is an open source parallel test execution tool does just that. Execute tests in parallel on multiple nodes on your testing cluster. Its master-slave architecture allows easy horizontal dynamic scaling. In other words, it’s a matter of adding more slaves to the cluster to speed up test execution. Furthermore, its intelligent job distribution engine leverages past job execution metrics to make future runs even faster. In this post I will discuss how you are going to break down your testing suite and configure ClusterRunner. But before we go into installation and setup, let’s look at how ClusterRunner works.

HOW CLUSTERRUNNER WORKS

ClusterRunner can be started using two modes: master and slave mode. Master will act as a server and slaves will be connected to the cluster master. When master is up, you can submit a build job to it. This build job will contain information about where your project’s repository is located and in what branch the test suite should be executed. Cluster master will pull your project and will read the clusterrunner configuration file in it. This ClusterRunner config file dictates as to how your tests should be divided (atomized in ClusterRunner terms) among the online slaves and what commands should be invoked to run a test. Once the atomization (creation of atoms) phase is done, slaves will fetch your project and run any configured scripts defined in the clusterrunner config file, before running any tests. Once these prep scripts done executing, master will distribute atoms among the slave nodes one by one. An Atom can be a name of a test class or group of related tests. When a slave receives an atom, it will execute the configured commands on that particular atom and send any generated files by the test (test artifacts) back to the master. This process repeats until all of the atoms done processing and finally the build artifacts will be published so your CI can parse the test results and present nicely! This whole process can be summed up with the following diagram.

CLUSTERRUNNER

Now that you have some idea about what’s happening under the hood, we will see how to setup ClusterRunner under linux environment. You can follow along this tutorial even if you have a single VM, although you will need more than one VM to see parallel execution of tests.

mkdir -p ~/.clusterrunner/dist && cd ~/.clusterrunner && curl -L https://cloud.box.com/shared/static/2pl4pi6ykvrbb9d06t4m.tgz > clusterrunner.tgz && tar -zxvf clusterrunner.tgz -C ./dist && cp ./dist/conf/default_clusterrunner.conf clusterrunner.conf && chmod 600 clusterrunner.conf

This will put ClusterRunner binaries inside .clusterrunner/dist directory on your home directory. *Each slave VM must have the same username of the master VM. (ClusterRunner does not support running multiple slave instances in the same VM) Master and slaves needs the ability to passwordless ssh communication. To enable passwordless authentication on master, include master’s public key in each slave’s authorized_keys file under the .ssh directory (www.linuxproblem.org/art_9.html). Repeat this step for all other slaves. You also have to set SSH keys of master and slaves on the Git server. Proper hostname mappings between master and slaves must exist as the ClusterRunner uses hostname to perform ssh commands. *Master and slave machines must use the same operating system.

These binaries have to be copied to all salves in the cluster. Since this is tedious process when number of slaves are high, ClusterRunner has provided the deploy command to automate this process. To deploy binaries to all the slaves issue the following command:

clusterrunner deploy --slaves hostname1 hostname2 hostname3

If this command executed successfully you can see that each salve’s home directory has the ClusterRunner binaries copied inside the ~/.clusterrunner/dist .

SETTING UP YOUR TEST PROJECT

Now that the ClusterRunner is deployed into the master and the slave machines it’s time to write some tests. We are going to create a simple maven java project and write some test classes. Create a simple maven project by following command:

mvn archetype:generate -DgroupId=com.thilanka -DartifactId=testapp -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false

Let’s add some test classes to simulate long running tests (I’m using TestNG but you can use junit or any other testing framework):

TestDemoA.java

package clusterrunner;

    import org.testng.Assert;

    import org.testng.annotations.Test;

    /**

     * Created by Thilanka Nuwan Liyanaarachchi

    */

    @Test(singleThreaded = true)

    public class TestDemoA {

        @Test

        public void testFeature1() throws Exception {

            Thread.sleep(12000);

            Assert.assertEquals(4, 4, "Error in TestDemoA.testFeature1");

        }
@Test

    public void testFeature2() throws Exception {

    Thread.sleep(3000);

    Assert.assertEquals("x", "x", "Error in TestDemoA.testFeature2");

    }

    }

    TestDemoB.java

    package clusterrunner;

    import org.testng.Assert;

    import org.testng.annotations.Test;

    /**

    * Created by Thilanka Nuwan Liyanaarachchi

    */

    @Test(singleThreaded = true)

    public class TestDemoB {

    @Test

    public void testFeature1() throws Exception {

    Thread.sleep(3000);

    Assert.assertEquals(4, 4, "Error in TestDemoB.testFeature1");

    }

    @Test

    public void testFeature2() throws Exception {

    Thread.sleep(22000);

    Assert.assertEquals("x", "x", "Error in TestDemoB.testFeature2");

    }

                    }

Add following dependencies in your  pom.xml :

<dependency>

        <groupId>org.testng</groupId>

        <artifactId>testng</artifactId>

        <version>6.11</version>

                   </dependency>

JOB CONFIGURATION

In the root of your project add the  clusterrunner.yaml file. Put the following content in that file:

Simple:

    setup_build:
     - export JAVA_HOME=/usr/java/jdk1.8.0_111

     - export MAVEN_OPTS="-Xmx8192m -Xms128m"

     - cd $PROJECT_DIR

     - mvn clean install -DskipTests

    teardown_build:
     - echo "Performing teardown"
    commands:

     - mvn test -Dtest=$TOKEN; mkdir -p $ARTIFACT_DIR/surefire-reports; rm -rf $ARTIFACT_DIR/surefire-reports/*; cp -r target/surefire-reports/* $ARTIFACT_DIR/surefire-reports

    atomizers:
     - TOKEN: java -cp ~/atomizer.jar com.thilanka.testapp.Atomizera

Let’s break this file down and see what each line does. Firstly this is a yaml file. Much like xml but more fun to work with The root element is specified as Simple. This name can be anything but let’s just keep it Simple  The   setup_build  section list downs commands that need to be executed. So there we are setting java home and some maven options. Finally we cd into the project directory by using the ClusterRunner variable and build our java project.  tear_down section is much like the setup_build section but the only difference is the commands specified in tear_down will only be executed when all of the tests are done executing. Now everything seems to be ready for running our tests. But before running any test, there should be a way to let ClusterRunner know as to how our tests should run in parallel. This criterion is defined in the  atomizers section. Don’t worry. I’m not skipping the  commands section but it makes more sense to explain the atomizers first. Atomization is just breaking down your suite of tests into smaller parts called atoms so that each atom can run in parallel on different slave machines. Here I have just written a simple java program that just prints the names of our two test classes to the standard output stream. The atomizer is a program that is executed by the ClusterRunner once in the beginning of a build which prints some variables to the standard out, line by line. Each line output of this program is fed into the TOKEN variable. The name of this variable can be anything. So now we have two atoms denoting the fully qualified names of the two classes (package+class name). Finally for each atom we can run set of commands on it. These commands are specified in the  commands section. As you can see we are running a single test class by the maven command: mvn test -Dtest= $TOKEN Here the token variable refers to the class name that we’ve atomized before. Oh and in case if you are wondering how the atomizer.jar code look like:

System.out.println(“clusterrunner.TestDemoA”);

                    System.out.println(“clusterrunner.TestDemoB”);

But in a real project your tests may be defined in a TestNG suite.xml file. If that’s the case your atomizer program should read the xml and extract each test class from that file. Well with this minimal configuration we are ready to run the two test classes in two different slave machines hopefully.

STARTING UP THE CLUSTER

We are going to fire up a master instance and two slave instances to run our first build. Let’s start the instances by issuing following commands:

Start master : ~/.clusterrunner/dist/clusterrunner master

    Start slave 1 : ssh cluster@myhost1 "~/.clusterrunner/dist/clusterrunner slave"

    Start slave 2 : ssh cluster@myhost2 "~/.clusterrunner/dist/clusterrunner slave"

*These commands are executed on the master host by ssh

Now the master and all slaves are ready to take any job. Let’s create a new job and run it.

RUNNING A JOB

The following build command (executed on the master machine) will run your tests:

~/.clusterrunner/dist/clusterrunner build git --url ssh://git@gitlab.thilanka.com:40456/tnl/testapp.git --branch "develop" --job-name Simple

Here it specifies the git repo url, the branch on which tests should run and the job name that we’ve specified in our clusterrunner.yaml file.

When the job is finished, any artifacts generated from tests are stored in each atom’s directory. These can be found under where the build command is executed.

Thilanka Liyanarachchi

Senior Software Engineer

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