The hub is the central point of a Selenium Grid. It has a registry of all the available nodes that are connected and part of a particular grid. The hub is a Selenium Standalone server running in the hub mode, listening on port 4444 of a machine by default. The test scripts will try to connect to the hub on this port, just as any Remote WebDriver. The hub will take care of rerouting the test-script traffic to the appropriate test-platform node. Let's see how we can start a hub node. Navigate to the location where you have your Selenium server JAR file and execute the following command:

java -jar selenium-server-standalone-3.12.0.jar -role hub

Doing this will start your server in the hub mode. By default, the server starts listening on port 4444; however, you can start your server on the port of your choice. Suppose you want to start the server on port...