Customizing a Node

How to customize a Node

There are times when we would like a Node to be customized to our needs.

For e.g., we may like to do some additional setup before a session begins execution and some clean-up after a session runs to completion.

Following steps can be followed for this:

  • Create a class that extends org.openqa.selenium.grid.node.Node

  • Add a static method (this will be our factory method) to the newly created class whose signature looks like this:

    public static Node create(Config config). Here:

    • Node is of type org.openqa.selenium.grid.node.Node
    • Config is of type org.openqa.selenium.grid.config.Config

  • Within this factory method, include logic for creating your new Class.

  • To wire in this new customized logic into the hub, start the node and pass in the fully qualified class name of the above class to the argument --node-implementation

Let’s see an example of all this:

Custom Node as an uber jar

  1. Create a sample project using your favourite build tool (Maven|Gradle).
  2. Add the below dependency to your sample project.
  3. Add your customized Node to the project.
  4. Build an uber jar to be able to start the Node using java -jar command.
  5. Now start the Node using the command:
java -jar custom_node-server.jar node \
--node-implementation org.seleniumhq.samples.DecoratedLoggingNode

Note: If you are using Maven as a build tool, please prefer using maven-shade-plugin instead of maven-assembly-plugin because maven-assembly plugin seems to have issues with being able to merge multiple Service Provider Interface files (META-INF/services)

Custom Node as a regular jar

  1. Create a sample project using your favourite build tool (Maven|Gradle).
  2. Add the below dependency to your sample project.
  3. Add your customized Node to the project.
  4. Build a jar of your project using your build tool.
  5. Now start the Node using the command:
java -jar selenium-server-4.6.0.jar \
--ext custom_node-1.0-SNAPSHOT.jar node \
--node-implementation org.seleniumhq.samples.DecoratedLoggingNode

Below is a sample that just prints some messages on to the console whenever there’s an activity of interest (session created, session deleted, a webdriver command executed etc.,) on the Node.

Sample customized node 
package org.seleniumhq.samples;

import java.io.IOException;
import java.net.URI;
import java.util.UUID;
import java.util.function.Supplier;
import org.openqa.selenium.Capabilities;
import org.openqa.selenium.NoSuchSessionException;
import org.openqa.selenium.WebDriverException;
import org.openqa.selenium.grid.config.Config;
import org.openqa.selenium.grid.data.CreateSessionRequest;
import org.openqa.selenium.grid.data.CreateSessionResponse;
import org.openqa.selenium.grid.data.NodeId;
import org.openqa.selenium.grid.data.NodeStatus;
import org.openqa.selenium.grid.data.Session;
import org.openqa.selenium.grid.log.LoggingOptions;
import org.openqa.selenium.grid.node.HealthCheck;
import org.openqa.selenium.grid.node.Node;
import org.openqa.selenium.grid.node.local.LocalNodeFactory;
import org.openqa.selenium.grid.security.Secret;
import org.openqa.selenium.grid.security.SecretOptions;
import org.openqa.selenium.grid.server.BaseServerOptions;
import org.openqa.selenium.internal.Either;
import org.openqa.selenium.io.TemporaryFilesystem;
import org.openqa.selenium.remote.SessionId;
import org.openqa.selenium.remote.http.HttpRequest;
import org.openqa.selenium.remote.http.HttpResponse;
import org.openqa.selenium.remote.tracing.Tracer;

public class DecoratedLoggingNode extends Node {

  private Node node;

  protected DecoratedLoggingNode(Tracer tracer, URI uri, Secret registrationSecret) {
    super(tracer, new NodeId(UUID.randomUUID()), uri, registrationSecret);
  }

  public static Node create(Config config) {
    LoggingOptions loggingOptions = new LoggingOptions(config);
    BaseServerOptions serverOptions = new BaseServerOptions(config);
    URI uri = serverOptions.getExternalUri();
    SecretOptions secretOptions = new SecretOptions(config);

    // Refer to the foot notes for additional context on this line.
    Node node = LocalNodeFactory.create(config);

    DecoratedLoggingNode wrapper = new DecoratedLoggingNode(loggingOptions.getTracer(),
        uri, secretOptions.getRegistrationSecret());
    wrapper.node = node;
    return wrapper;
  }

  @Override
  public Either<WebDriverException, CreateSessionResponse> newSession(
      CreateSessionRequest sessionRequest) {
    return perform(() -> node.newSession(sessionRequest), "newSession");
  }

  @Override
  public HttpResponse executeWebDriverCommand(HttpRequest req) {
    return perform(() -> node.executeWebDriverCommand(req), "executeWebDriverCommand");
  }

  @Override
  public Session getSession(SessionId id) throws NoSuchSessionException {
    return perform(() -> node.getSession(id), "getSession");
  }

  @Override
  public HttpResponse uploadFile(HttpRequest req, SessionId id) {
    return perform(() -> node.uploadFile(req, id), "uploadFile");
  }

  @Override
  public HttpResponse downloadFile(HttpRequest req, SessionId id) {
    return perform(() -> node.downloadFile(req, id), "downloadFile");
  }

  @Override
  public TemporaryFilesystem getDownloadsFilesystem(UUID uuid) {
    return perform(() -> {
      try {
        return node.getDownloadsFilesystem(uuid);
      } catch (IOException e) {
        throw new RuntimeException(e);
      }
    }, "downloadsFilesystem");
  }

  @Override
  public TemporaryFilesystem getUploadsFilesystem(SessionId id) throws IOException {
    return perform(() -> {
      try {
        return node.getUploadsFilesystem(id);
      } catch (IOException e) {
        throw new RuntimeException(e);
      }
    }, "uploadsFilesystem");

  }

  @Override
  public void stop(SessionId id) throws NoSuchSessionException {
    perform(() -> node.stop(id), "stop");
  }

  @Override
  public boolean isSessionOwner(SessionId id) {
    return perform(() -> node.isSessionOwner(id), "isSessionOwner");
  }

  @Override
  public boolean isSupporting(Capabilities capabilities) {
    return perform(() -> node.isSupporting(capabilities), "isSupporting");
  }

  @Override
  public NodeStatus getStatus() {
    return perform(() -> node.getStatus(), "getStatus");
  }

  @Override
  public HealthCheck getHealthCheck() {
    return perform(() -> node.getHealthCheck(), "getHealthCheck");
  }

  @Override
  public void drain() {
    perform(() -> node.drain(), "drain");
  }

  @Override
  public boolean isReady() {
    return perform(() -> node.isReady(), "isReady");
  }

  private void perform(Runnable function, String operation) {
    try {
      System.err.printf("[COMMENTATOR] Before %s()%n", operation);
      function.run();
    } finally {
      System.err.printf("[COMMENTATOR] After %s()%n", operation);
    }
  }

  private <T> T perform(Supplier<T> function, String operation) {
    try {
      System.err.printf("[COMMENTATOR] Before %s()%n", operation);
      return function.get();
    } finally {
      System.err.printf("[COMMENTATOR] After %s()%n", operation);
    }
  }
}

Foot Notes:

In the above example, the line Node node = LocalNodeFactory.create(config); explicitly creates a LocalNode.

There are basically 2 types of user facing implementations of org.openqa.selenium.grid.node.Node available.

These classes are good starting points to learn how to build a custom Node and also to learn the internals of a Node.

  • org.openqa.selenium.grid.node.local.LocalNode - Used to represent a long running Node and is the default implementation that gets wired in when you start a node.
    • It can be created by calling LocalNodeFactory.create(config);, where:
      • LocalNodeFactory belongs to org.openqa.selenium.grid.node.local
      • Config belongs to org.openqa.selenium.grid.config
  • org.openqa.selenium.grid.node.k8s.OneShotNode - This is a special reference implementation wherein the Node gracefully shuts itself down after servicing one test session. This class is currently not available as part of any pre-built maven artifact.
    • You can refer to the source code here to understand its internals.
    • To build it locally refer here.
    • It can be created by calling OneShotNode.create(config), where:
      • OneShotNode belongs to org.openqa.selenium.grid.node.k8s
      • Config belongs to org.openqa.selenium.grid.config
Last modified April 3, 2023: Updating sample code for node customisation (#1352) (7771c573bf)