AZR - Function App

 Azure Functions provides "compute on-demand" - and in two significant ways.

First, Azure Functions allows you to implement your system's logic into readily available blocks of code. These code blocks are called "functions". Different functions can run anytime you need to respond to critical events.

Second, as requests increase, Azure Functions meets the demand with as many resources and function instances as necessary - but only while needed. As requests fall, any extra resources and application instances drop off automatically.

Azure Functions has 3 pricing plans

• Consumption plan: Azure provides all of the necessary computational resources. You don't have to worry about resource management, and only pay for the time that your code runs.
  -Pay only when your function(s) are running
  -Scale out/in as and when required 

• Premium plan: You specify a number of pre-warmed instances that are always online and ready to immediately respond. When your function runs, Azure provides any additional computational resources that are needed. You pay for the pre-warmed instances running continuously and any additional instances you use as Azure scales your app in and out.

• App Service plan: Run your functions just like your web apps. If you use App Service for your other applications, your functions can run on the same plan at no additional cost.

          Session Affinity