What is Selenium Grid and why is it used?

Selenium Grid allows running Selenium tests on multiple machines (nodes) simultaneously, controlled by a central Hub. It enables parallel execution and cross-browser/cross-OS testing at scale.

Architecture:

• ✓Hub — central controller that receives test requests and routes them to nodes
• ✓Node — machines that execute the actual tests in different browsers/OS

Why use Selenium Grid:

• ✓Parallel execution — run many tests at once, much faster
• ✓Cross-browser testing — Chrome, Firefox, Edge, Safari simultaneously
• ✓Cross-OS testing — Windows, Linux, macOS in one run
• ✓Scalable — add more nodes for more capacity

Selenium 4 Grid — standalone setup:

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

Connect tests to Grid:

ChromeOptions options = new ChromeOptions();
RemoteWebDriver driver = new RemoteWebDriver(
    new URL("http://localhost:4444"),
    options
);

Cloud alternatives: BrowserStack, Sauce Labs, LambdaTest — managed Selenium Grid as a service, no maintenance needed.