By default, a web app created using App Service can only be accessed through the internet. But there are many cases when you’d want to be able to connect to an app in different ways. For example, you might want an app to only be accessible internally rather than over the internet, or you might want to connect the app to a database in either Azure or an on-premises environment.

There are many different ways to connect to or from an app, depending on exactly what you need to do. These methods can be divided into two groups: inbound (for connecting to an app) and outbound (for connecting from an app to other resources).

We’ll start with the inbound methods. If you’re okay with your app communicating over the internet, but you want to restrict which IP addresses can connect to it, then the easiest way to do that is to add access restriction rules to your app. Each rule either allows or denies access to a single IP address or a block of IP addresses.

If you have resources in an Azure virtual network that need to connect to your app over the Microsoft backbone network rather than over the internet, then you can restrict access to your app using a service endpoint rather than an IP address. A service endpoint is something you can enable on a subnet. So you can create a service-endpoint-based rule that allows access to your app from a particular subnet in a VNet.

A newer way of doing this is to create a private endpoint for your app. This is a private IP address in your VNet that gets attached to your app. One advantage of using a private endpoint is that it makes it easy to connect to your app from an on-premises environment. If you already have a connection from your on-premises environment to your Azure VNet using a method such as Azure ExpressRoute or Azure VPN, then you can connect to the app through the private endpoint in the VNet. This is more difficult to do with a service endpoint. For this and other reasons, Microsoft recommends using private endpoints rather than service endpoints.

All of the methods I’ve mentioned so far have been for controlling inbound connections to your app. To allow your app to initiate outbound connections to various resources, we need to use different methods. An outbound connection is typically used to connect an app to a database or other type of supporting resource.

App Service Hybrid Connections is a feature that allows an app to connect to a resource in an Azure virtual network or an on-premises environment. To make it work, you need to install Hybrid Connection Manager on a Windows Server that has access to both networks over port 443. App Service then uses this as a relay to connect to the other environment. The advantage of using Hybrid Connections is that it provides secure access even if you don’t have an ExpressRoute or VPN connection between your on-premises environment and Azure.

Another method is called VNet Integration. There are two different types: Regional VNet Integration and Gateway-required VNet Integration. The great thing about the Regional method is that you don’t need to install anything.

To configure it in App Service, you go into the Networking section of your app’s configuration and select VNet Integration. Then you just need to tell it which VNet you want to add. If the VNet that you want to integrate with is in the same region as the app, then the only requirement is that the VNet has to have an empty subnet that the Integration feature can use.

Once you’ve configured Regional VNet Integration, then your app can connect to resources in the VNet or in an on-premises network that’s connected to the VNet through ExpressRoute or a VPN. It can even connect to a VNet in a different region if there’s a peering connection between that VNet and the regional VNet.

Pretty much the only reason you’d need to use Gateway-required VNet Integration is if your app needs to connect to a VNet in another region that isn’t peered with a regional VNet. In that case,  you’d need to install a virtual network gateway in the remote VNet. This method has a number of disadvantages, though, such as not allowing connections to on-premises environments over ExpressRoute. So, in most cases, it’s better to use Regional VNet Integration than Gateway-required VNet Integration.

And that’s it for configuring networking in Azure App Service. Please give this course a rating, and if you have any questions or comments, please let us know. Thanks!