A Web role is a Virtual Machine instance on which 'Windows Server with IIS' is running.
Typically, a Web role is created for the front-end of Web applications and Web services. Developers can use ASP.NET Web Forms, or MVC applications or Windows Communication Foundation (WCF) to develop a Web role. An application deployed in a web role can be implemented with any technology that works with IIS, which means that we can create applications using Java, PHP and Node.js and deployed them.
Refer figure. Observe that there is a box on the left side and one on the right side. The left one is an instance of web role Virtual machine. The operating system windows server is installed on this VM instance. On this Windows server, IIS is installed. An application is hosted on this web role instance. The web role instance is a front end of the application and can take requests from the user.
After taking requests azure places these requests in queues and worker roles picks these requests and processes them.
Remember, a single instance of a web role is assigned to a single VM, and no other applications will be assigned to that VM. In this way, azure ensures that every instance of your web application is isolated from other applications running on the same physical server.
Windows Server OS with IIS
A windows server OS is an operating system is designed to operate a network of computers.
IIS is now expands to Internet Information services and is a web server software and offers services of a web host. You can run web applications on your desktop with the help of IIS.
Windows Communication Foundation
It is a framework for building service based applications based on the service oriented architecture. This framework provides security, reliable queuing of service messages, REST support and extensibility features for enhancing your applications.
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