Setting Up Selenium Grid for Distributed Testing

Introduction

As test suites grow, running Selenium tests on a single machine becomes slow and inefficient. Selenium Grid enables distributed test execution by allowing tests to run in parallel across multiple machines, browsers, and operating systems. This significantly reduces test execution time and improves cross-browser coverage.

1. What Is Selenium Grid?

Selenium Grid is a component of Selenium that allows you to:

Run tests in parallel

Execute tests on different browsers and OS combinations

Distribute test load across multiple machines

Selenium Grid follows a Hub–Node architecture (or a simplified unified architecture in Selenium 4).

2. Selenium Grid Architecture

Selenium 4 (Recommended)

Selenium 4 introduces a standalone Grid with simplified setup:

No separate hub and node commands required

Built-in session management

Better scalability and observability

Key Components

Hub: Central point that receives test requests

Node: Machine that executes tests

Router, Distributor, Session Map: Internal services managing test sessions

3. Prerequisites

Before setting up Selenium Grid, ensure:

Java JDK 11 or later

Selenium Server JAR (Selenium 4)

Browsers installed (Chrome, Firefox, Edge)

Browser drivers (ChromeDriver, GeckoDriver)

Network connectivity between machines

4. Download Selenium Server

Download the Selenium Server JAR from the official Selenium website.

Example:

selenium-server-4.x.x.jar

5. Setting Up Selenium Grid (Standalone Mode)

Step 1: Start Selenium Grid

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

This command:

Starts the Grid

Automatically registers local browsers

Acts as both Hub and Node

Step 2: Access Grid UI

Open a browser and go to:

http://localhost:4444

You can view:

Registered nodes

Available browsers

Active sessions

6. Running Tests on Selenium Grid

Example Test Configuration (Java)

DesiredCapabilities caps = new DesiredCapabilities();

caps.setBrowserName("chrome");

WebDriver driver = new RemoteWebDriver(

new URL("http://localhost:4444"),

caps

);

Your tests will now run on the Grid instead of locally.

7. Distributed Setup (Multiple Machines)

Step 1: Start the Hub

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

Step 2: Start Nodes

On each node machine:

java -jar selenium-server-4.x.x.jar node --hub http://<hub-ip>:4444

Each node registers itself with the Hub.

8. Running Tests in Parallel

Use a test framework that supports parallel execution:

TestNG Example

</classes>

</test>

</suite>

This allows multiple tests to run simultaneously.

9. Using Docker for Selenium Grid

Docker simplifies Grid setup and scaling.

Start Grid with Docker

docker run -d -p 4444:4444 selenium/standalone-chrome

For multi-browser setups, use Docker Compose with official Selenium images.

10. Best Practices

Use Selenium 4 standalone mode for simplicity

Match browser and driver versions

Enable parallel execution gradually

Monitor Grid performance and logs

Clean up sessions after test execution

11. Common Issues and Troubleshooting

Issue Solution

Browser not launching Check driver compatibility

Tests timing out Increase session timeout

Node not registering Verify network and ports

Slow execution Add more nodes

12. Benefits of Selenium Grid

Faster test execution

Scalable test infrastructure

Better browser coverage

CI/CD integration support

Conclusion

Selenium Grid is a powerful solution for scaling automated testing across environments. With Selenium 4’s simplified architecture, setting up distributed testing is easier than ever. Whether running locally, across multiple machines, or in Docker, Selenium Grid helps teams achieve faster and more reliable test automation.

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December 28, 2025