What is Selenium Grid?

Selenium Grid is a tool that helps in distributed running of test scripts across different machines having different browsers, browser versions, and platforms — all in parallel.

Architecture:

• ✓Hub — the central server that manages all distributed machines (nodes). It receives test requests and assigns them to available nodes.
• ✓Node — the machines attached to the hub where tests actually execute.

         [Hub - Central Server]
         /          |          \
   [Node 1]    [Node 2]    [Node 3]
   Chrome      Firefox      Safari
   Windows     Linux        macOS

Benefits:

1. ✓Parallel execution — multiple tests run simultaneously, drastically reducing total test time
2. ✓Multi-browser testing — run on Chrome, Firefox, Edge, Safari at the same time
3. ✓Multi-platform testing — run on Windows, Linux, macOS simultaneously
4. ✓Scalable — add more nodes to handle more tests

Selenium 4 Grid — Quick start:

# Standalone mode (hub + node in one)
java -jar selenium-server-4.x.jar standalone

# Or hub mode
java -jar selenium-server-4.x.jar hub

# And on another machine start a node
java -jar selenium-server-4.x.jar node --hub http://hub-ip:4444

Connect test to Grid:

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