Assume that you're working on a project that requires testing on multiple configurations. What are you going to do? Running different scripts on each and every device is cumbersome. Automation Testing will help you save time and manual efforts. As an automation tester, you should know about Selenium grid.
This is exactly why Selenium Grid is built. It can help you test on all major browsers, all major operating systems, and even on mobile device browsers. You can get a huge browser coverage in all your functional tests ensuring the perfect experience for a wide range of your potential users.
What Is Selenium Grid?
Selenium Grid allows parallel testing against various browsers & OS combinations through a Client-Server model. Here, the Server is known as the Hub which has multiple Clients to interact with. With Selenium Grid, you can connect a server to multiple remote machines which can then be used to run a browser automation script over multiple browsers + OS configurations, simultaneously.
How Selenium Grid Works?
Selenium Grid is comprised of two concepts:
Hub: It is the center of the Selenium Grid architecture that manages the network of the test machines. There is only one hub in a network that is assigned to a test of Desired Capabilities(operating system, browser, browser versions) and then the hub finds the test that matches the given configurations. A Selenium Hub is referred to as the server.
Nodes: Nodes are the test machines that execute the test that was earlier loaded on the hub. There can be multiple nodes configured with a different operating system and different browsers. It is not mandatory for the node to run on the same platform on which the hub is running. Selenium nodes are referred to as clients connected to a server.

How to Configure Selenium Grid?
- Ensure that your system has Java Runtime Environment (JRE) or better
yet Java Development Kit (JDK) installed. Though most people
recommend going for the latest JDK, I prefer earlier tried and
tested versions like JDK SE 08 or 09. You can go for the latest one
if you wish.
- Download and extract Selenium Standalone server JAR files from here.
If you are willing to learn Selenium Grid from scratch, then check out this Selenium Grid tutorial.