Azure App Service supports connecting to Application (App) Server and Database (DB) Server hosted in Azure VM or on-premise server using vNET integration that is part of App Service Plan(ASP). You get such scenarios often if you are migrating your applications landscape to Azure from on-premise. You will have different scenarios like shared DBs or may be DB team is not ready yet to DBs to PaaS, or there is no PaaS DB service available for the like of DB2, Oracle database services. App Service vNET integration is a useful feature if you do not chose to go with App Service Environment (ASE).
When you configure the vNET integration, your WebApp will get private IP from the vNET. App Service will be able to communicate with a VM in the vNET or another vNET peered in the same region, or a server on-premises over express route or s2s VPN.
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