Azure Compute infrastructure is a sophisticated environment and includes several components which work together to run Azure applications. The figure depicts Azure compute environment.
Below are the salient points describing how the Azure compute environment operates.
All cloud vendor provides an environment to run the applications and the environment is called compute environment.
The Azure compute (runtime) environment includes web role and worker role instances, load balancer and fabric controller.
Users make requests to an application and load balancer forwards these requests to web roles and worker roles.
When a fault occurs, Fabric Controller creates a new instance and load balancer identifies the new instance.
Developers can increase or decrease the number of instances either by using Windows Azure portal or by programmatically using APIs.
Web Role: A web role instance is a VM instance which runs specific version of Windows server and IIS, runs your web application and used for front-end of the web application.
Worker role: A worker role instance is also a VM instance which runs specific version of Windows server and used for backend processing. The worker role instance does not include IIS.
Queues are used for communication between web roles and worker roles.
Worker role persists data in Windows Azure Storage or SQL database whichever is the chosen database management option.
The word backend is used in many industries. In a take away restruarant backend processing is what happens in the kitchen where the supervisor processes an order. In a automobile company, an example of backend processing is the activity of calculating the orders received from the dealers and coming out with estimates for planning immediate future activities. Back end processing is time consuming task and is separated from the front end processing to ensure that front end processing goes on without interruption. When Azure application is working the front end is always ready to receive inputs from the users without interruption. To ensure this, the worker roles take up the backend processing and manage all the tasks.
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