Selenium Grid and CI

What is Selenium Grid 4 and what are its components?

Grid runs tests on remote machines and browsers in parallel. Grid 4 can run as standalone (all in one), hub and node, or fully distributed with these components:

Component	Role
Router	entry point; forwards requests
Distributor	assigns a new session to a node with free slots
Session Map	remembers which node owns which session
New Session Queue	holds requests while all slots are busy
Event Bus	messages between components
Node	runs the browsers

Example

java -jar selenium-server-4.25.0.jar standalone

Example output

INFO [Standalone.execute] - Started Selenium Standalone 4.25.0 (revision 8a8aea2337): http://192.168.1.10:4444

How do you run a test on Grid?

ChromeOptions options = new ChromeOptions();
options.setPlatformName("linux");
WebDriver driver = new RemoteWebDriver(URI.create("http://grid.qa.local:4444").toURL(), options);
driver.get("https://shopease.example.com");

Use RemoteWebDriver with the Grid URL and browser options. For parallel runs, keep the driver in a ThreadLocal and set parallel and thread-count in testng.xml. Docker images (selenium/hub, selenium/node-chrome) are the easiest way to host a Grid.

How do you run Selenium tests in a CI pipeline?

The pipeline checks out the code, sets up JDK and Maven, and runs mvn clean test -DsuiteXml=testng-smoke.xml -Dheadless=true.
Browsers run headless on the agent, or on a Selenium Grid / cloud grid via RemoteWebDriver.
Secrets (passwords, access keys) come from CI secrets as environment variables.
Reports and screenshots are archived (upload-artifact / publishHTML) even on failure.
Triggers: smoke on every pull request, full regression on a nightly cron.