How to add Azure App Service redundancy using Application Gateway?

Question

what is the recommended best practice for using Azure Application Gateway with redundant app services (in either different regions or availability sets)? I've had some issues recently where our app service would occasionally go down for a couple minutes (due to maintenance in msft's data center) and I'd like to have our app gateway redirect load to another instance or app service when this happens.

Currently traffic is handled as such: public request -> app.example.com -> app gateway -> app.example.com -> backend app service.

I've been unable to add a second app service because when I attempt to do so I get the error "Hostname is already being used in the following App: myappservicename. Please remove the Hostname from myfirstappservice, and try again" when I attempt to add the custom domain to a second app service. It seems my custom domain would need to be added to each individual app service in order for traffic to be routed properly to my backend web app. Or is there another way I should have traffic configured?

Answer 1

You should bind your custom domain to your app gateway only and add your two app services into a backend pool so that the traffic could be:

public request -> app.example.com -> app gateway ->backend pool(handled by one of your 2 app services)

which meets your requirement.