Selenium Grid 4: Features, Setup, and Parallel Execution Explained

Selenium Grid has always been a powerful tool for running automated tests across multiple machines, browsers, and operating systems. With the release of Selenium Grid 4, the Selenium team introduced a completely redesigned architecture, modern protocols, enhanced stability, and simplified configuration. Whether you're building a scalable automation ecosystem or optimizing execution speed, Selenium Grid 4 helps you achieve consistent, fast, and distributed test execution.

In this article, we explore the key features, setup process, and parallel execution capabilities of Selenium Grid 4.

What Is Selenium Grid 4?

Selenium Grid 4 is the latest version of the Selenium Grid system that allows testers to run automated tests on distributed environments. It lets you execute tests in parallel across multiple nodes (machines), browsers, and versions—improving both execution speed and test coverage.

Unlike earlier versions, Selenium Grid 4 brings a more stable, unified, and cloud-ready design that aligns with modern testing needs and CI/CD workflows.

Key Features of Selenium Grid 4

1. New and Improved Architecture

Selenium Grid 4 introduces a fully distributed, semi-distributed, and standalone mode. The architecture consists of:

• Event Bus

• Session Map

• Distributor

• Router

• Nodes

This modular structure increases flexibility, scalability, and reliability compared to Grid 3.

2. Supports W3C WebDriver Protocol

Selenium Grid 4 now relies completely on the W3C WebDriver standard, ensuring:

• Better compatibility across browsers

• More predictable test behavior

• Reduced flakiness

• Simplified communication between client and grid

This is a massive upgrade from the JSON Wire Protocol used earlier.

3. New User-Friendly UI

Grid 4 comes with a modern, intuitive dashboard that shows:

• Active sessions

• Available nodes

• Node configurations

• Browser usage

This makes monitoring test execution easier, especially in large distributed environments.

4. Built-In Observability

Selenium Grid 4 integrates observability tools like:

• OpenTelemetry

• Tracing & logging improvements

• Grid-wide metrics

These help diagnose failures faster and provide deeper performance insights during test execution.

5. Docker & Kubernetes Support

Grid 4 works seamlessly with:

• Docker containers

• Docker Compose

• Kubernetes clusters

This enables you to create scalable, containerized test environments ideal for DevOps pipelines.

6. Fully Backward Compatible

Existing Selenium 3 tests run smoothly with Grid 4. No major code changes are required, making migration easy.

How to Set Up Selenium Grid 4: Step-by-Step Guide

Selenium Grid 4 can be configured in 3 modes. Here we’ll walk through the simplest approach—Standalone mode, and then a hub and node setup using the distributed mode.

A. Setup in Standalone Mode (Beginner Friendly)

This mode combines Hub + Node in a single machine.

Step 1: Download Selenium Server

Download the Selenium jar file from the official Selenium website.

Step 2: Start Grid in Standalone Mode

Run the following command:

java -jar selenium-server-4.x.x.jar standalone

Step 3: Open Grid Dashboard

Navigate to:

http://localhost:4444/ui

You will see your Grid up and running, ready to accept sessions.

B. Setup in Distributed Mode (Hub + Multiple Nodes)

This mode is ideal for parallel and cross-browser testing at scale.

Step 1: Start the Event Bus

java -jar selenium-server-4.x.x.jar event-bus

Step 2: Start the Sessions Map

java -jar selenium-server-4.x.x.jar sessions

Step 3: Start the Distributor

java -jar selenium-server-4.x.x.jar distributor --sessions http://localhost:5556 --events http://localhost:5557

Step 4: Start the Router (central entry point)

java -jar selenium-server-4.x.x.jar router --sessions http://localhost:5556 --distributor http://localhost:5553

Step 5: Start Nodes

java -jar selenium-server-4.x.x.jar node --detect-drivers true --publish-events http://localhost:5557 --subscribe-events http://localhost:5558

Step 6: Monitor Grid

Open:

http://localhost:4444/ui

You can now connect many nodes, browsers, and configurations.

Parallel Test Execution in Selenium Grid 4

One of the biggest advantages of Selenium Grid is parallel execution—running multiple test cases at the same time across different machines and browsers.

How Parallel Execution Works

Each Node in Selenium Grid can run multiple sessions depending on:

• CPU cores

• RAM

• Browser instances available

When a test is triggered:

1. The Router receives the request

2. The Distributor checks for available nodes

3. The Node starts a browser session

4. The test runs in parallel with other sessions

This dramatically reduces execution time.

Example: Parallel Execution in TestNG

Below is a sample TestNG XML supporting parallel test execution:

<?xml version="1.0" encoding="UTF-8"?>
<suite name="Parallel Tests" parallel="tests" thread-count="3">
    <test name="Chrome Tests">
        <parameter name="browser" value="chrome"/>
        <classes>
            <class name="tests.GridTest"/>
        </classes>
    </test>

    <test name="Firefox Tests">
        <parameter name="browser" value="firefox"/>
        <classes>
            <class name="tests.GridTest"/>
        </classes>
    </test>
</suite>

This will run both Chrome and Firefox tests simultaneously on available Grid nodes.

Benefits of Using Selenium Grid 4 for Parallel Execution

1. Faster Test Execution

Multiple tests run simultaneously, reducing the total execution time from hours to minutes.

2. Better Test Coverage

You can test:

• Browsers (Chrome, Firefox, Edge, Safari)

• Browser versions

• Platforms (Windows, Mac, Linux)

—all at once.

3. Efficient Resource Utilization

Grid distributes load across nodes using a smart scheduler, reducing bottlenecks.

4. Ideal for CI/CD Pipelines

Selenium Grid 4 integrates well with:

• Jenkins

• GitLab CI

• GitHub Actions

• Azure DevOps

This automates parallel executions on every code commit.

Conclusion

Selenium Grid 4 is a powerful upgrade that gives test automation teams the ability to scale, distribute, and accelerate their test execution. With its redesigned architecture, W3C WebDriver support, Docker/Kubernetes compatibility, and improved observability, Grid 4 makes parallel testing more reliable and accessible than ever.

Whether you're a QA engineer, automation architect, or DevOps professional, adopting Selenium Grid 4 can significantly improve productivity and reduce test execution time—making it an essential component of any modern automation framework.