HI @SG ,
As far as I know Azure App Service is not serverless, but you can leverage it on serverless by using Azure Function, also if you check the Azure App Service plans, each plan defines the region, number of VM instances etc...
For more information, see:
App Service overview
https://learn.microsoft.com/en-us/azure/app-service/overview
Azure App Service plan overview
https://learn.microsoft.com/en-us/azure/app-service/overview-hosting-plans
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Best regards,
Leon