How to Setup a Hub and Node for Selenium Grid

How to Setup a Hub and Node for Selenium Grid
  • Selenium Grid allows us to execute our tests in multiple machines (physical / virtual) and multiple browsers with different versions, which dramatically speeds up test execution and helps in reducing total amount of time required for test execution.
  • For example, if we have a script that takes 100 minutes to execute sequentially , we could break that down to 10 short tests script run across 10 machines, and can complete them in 10 minutes without copying your test code to the other machine.
  • To get started with Selenium Grid, make sure you have Java installed and configured it and For selenium, you need to download selenium server and place it in a directory.
  • A grid consists of a single hub, and one or more nodes, Hub and Node are the two main elements that you come across when using grid
  • Hub the Hub is the central point which will receive all the test requests along with information on which browser, platform (i.e. WINDOWS, LINUX, etc) and where the test should be run. Based on the request received, it will distribute them to the registered nodes.
  • To start a hub with default parameters, we can run the below command from a command-line. Just navigate to the directory where your selenium jar file is available and execute the below statement. You can open command prompt from the same folder using 'Press Shift and Right Click' you see an option 'Open command window here'.

  • In the above statement, we have started Hub using default parameters, So the default port will be 4444 and Hub listen for new requests is port 4444. This is why port 4444 was used in the URL for locating the hub. You can also change the default port, by adding the optional parameter -port when you run the command example: -port 5555.
  • After starting the hub, we can view the status of the hub by opening any browser window and navigating
    If you have used any other port, you need to mention that port value instead of default port 4444.

  • Nodes are where our tests will run, each Node is machine (can be a physical machine / virtual machine) that we register with the Hub, when we register Node, Hub will get to know about the node, and it will display browser and configuration details of the node that we used to register node with parameters.
    Below is the command to register node with a Hub. If we are not specifying any parameters when starting node, it defaults to 5555 whenever "-role" option is provided and is not hub

  • After executing above command, you should see something like below. When the hub is running in the same machine, we use ‘localhost’ for node. If Hub and Node are running on separate machines, we have to register Node using the hostname of the remote machine running the hub.

  • By default, when we start the node, it starts total 11 browsers : 5 Firefox, 5 Chrome and 1 Internet Explorer and it has same set of browsers for Selenium Remote Control (legacy). The maximum number of concurrent tests is default to 5.
  • We can change this and other browser settings as well by passing the parameters to each -browser switch (each switch represents a node based on your parameters). If you use the -browser parameter, the default browsers will be ignored and only what you specify command line will be used. The node can be configured in two different ways, One is by specifying command line parameters, the other is by specifying by a json file. We will discuss more in detail on these parameters in next articles.
  • For now, this is how it looks when we register without specifying any parameters

  • When you mouse hover on the browser icons, it will show config information, here "seleniumProtocol": "Selenium" which provides the mechanism for Selenium RC (Remote control / Selenium 1) and "seleniumProtocol": "WebDriver" is for Selenium WebDriver. After registering the node, You can see the difference in grid console as above.
  • We have done with starting the Hub and Registering Nodes with the Hub. Now we need to run our tests with Selenium Grid, For webdriver nodes, we need to use the RemoteWebDriver and DesiredCapabilities object to define which browser, version of the browser and platform (OS - Windows / LINUX etc) that we want to run our tests.
  • Based on preferences that we set in the DesiredCapabilities instance, the Hub will point our tests to a node that matches with these preferences. If we specify capabilities that do not exist on our grid then there will be no match and the test will fail to run.
  • Why we need to use RemoteWebdriver Not the webdriver?
    If we use driver (FirefoxDriver / ChromeDriver / or other) not RemoteWebDriver, it will just assume that the communication to the browser is local. Example: - Webdriver driver = new FirefoxDriver(); Using this, driver will access Firefox browser which is available on the local machine.
    If we use RemoteWebDriver, it requires us to specify where the Selenium Server is located and on which web browser we want to execute our tests. For example,

  • Here in above statement , it is specified that Selenium Server is running on localhost with the default port 4444 and execute on firefox browser. In the same fashion, we can run selenium server on one machine as Hub and execute selenium tests on other machine by registering to the node by specifying parameters.
  • In the below example, Hub will point the test to a node which is running on the Windows machine (local machine) with Firefox browser as my node is executing in windows machine and capabilities specified is Only firefox browser.

  • In the above test, BeforeClass method open firefox browser and , verifies page title of google. Once done, it will quit the remote webdriver.
    Below is the testng.xml file :

  • After executing test as TestNG, you can view the console for details such as on which browser the tests are executed along with version and platform details if specified any.

  • In this tutorial we will see 'Parallel execution of tests' using selenium grid and execute tests on firefox and chrome browser.
  • We will register multiple nodes to the Hub and execute tests in parallel. In the below example we will register a node in the same local machine where hub is running and other node in remote machine.
  • We will register node 1 in local machine with the below command:
    java -jar selenium-server-standalone-2.48.2.jar -role node -hub
  • We will register node 2 with the below command in remote machine. In the below command, need to pass a parameter by passing JVM properties using the -D flag along with chrome driver path , so that when ever there is a request to execute in chrome driver, Hub will send the request to this node. And here we have to mention the IP address of the machine where the hub is running as we are starting this node in remote machine.
  • java -jar selenium-server-standalone-2.48.2.jar -role node -hub
    After executing the above command, console should look like below:

  • When a Hub receives request to execute test in Chrome browser and If we don't specify chrome driver path for node, it will throw an exception as "Exception: The path to the chromedriver executable must be set by the system property;
  • The latest version can be downloaded from
  • Now when these two nodes are registered to the hub, hub console should look like below :

  • And the Grid console should look like below which shows configuration details of the nodes with IP address. In the below image below image Node 1 is running in Windows * machine (WIN8_1) and Node 2 is running in Windows7 machine.

  • In order to do this, we will create two classes which has multiple @Test methods in it. And a Browser class which invokes the remote webdriver based on the browser parameter that we pass in testng.xml file
    First create a class as ''

  • We will call 'getDriver' method which will intern call 'getBrowserCapabilities' based on browser parameter from the below two classes. If we pass 'chrome' as parameter, it is invoke chromedriver
    Let us create a class as '' as below:

  • Let us create a class as '' as below:

  • Now to execute these tests, we need to create testng.xml file as below and set parallel="tests" with parameter browser for each test

  • Once we execute the above code, hub console will display information such as on 'number of nodes available', on which node it has started executing the tests etc.. as below :

  • There are many other parameters for browser settings that we can pass when registering node to hub. When ever we use -browser parameter, the default browsers will be ignored and only what we specify in command line will be used.
    Example :

  • After executing the above command, if you check the grid console, it will just show the browserName, browser version, Max instances (number of instances of same version of browser you can run over the Remote System) and the platform (OS running on the node) that we have used to register the node. Grid console looks like below :

  • If the remote machine has multiple versions of Firefox, We can map the location of each binary to a particular version on the same machine to execute with multiple versions as below: