Azure App Services - cannot locate child app created under its parent

Question

I have a web app with a child app created under Configuration => Path Mappings. The parent app's path is "site\wwwroot" and the child's is "site\wwwroot\app", configured as an application with preload enabled.

The problem is that I can't find this new app anywhere. Copilot tells me it should be listed in App Services, but it isn't. Having given up on finding it, I eventually got my publish profile right and was able to publish it, but I get the error:

HTTP Error 500.35 - ANCM Multiple In-Process Applications in same Process

This suggests to me that both parent and child apps are using the same app pool, although this answer from Microsoft says something different:

https://learn.microsoft.com/en-us/answers/questions/134462/http-error-500-35-ancm-mulitple-in-process-applica

It would help if I could find the child app's settings, but where are they?

Answer 1

Hi @kejiz23

The reason you're not seeing your "child app" separately listed in Azure App Services is because it isn’t actually a separate App Service. When you add an app under Configuration > Path Mappings (also called a virtual application), it lives inside your main (parent) App Service. It's just a folder in the site's file structure that is configured to behave like an application, but it's still part of the same web app and App Service Plan. That's why you don't see a separate app for it, it’s configured within the same App Service instance.

About the error you're hitting:

HTTP Error 500.35 - ANCM Multiple In-Process Applications in Same Process

This happens because you can't run multiple in-process ASP.NET Core apps inside the same IIS process. Since your parent and child app are both ASP.NET Core apps (and likely both configured for in-process hosting), they conflict inside the same w3wp.exe process.

To resolve this, make sure the parent and child apps are set up to run in separate application pools. You can do this by creating a new app pool just for the child app, and setting it to "No Managed Code", since ASP.NET Core uses its own runtime and doesn’t rely on the .NET Framework pipeline. You can also change the hosting model from InProcess to OutOfProcess in the child app (or both apps)

Kindly refer to the below documentations for better understanding:
Troubleshoot ASP.NET Core on Azure App Service and IIS
Advanced configuration of the ASP.NET Core Module and IIS

Hope this information is helpful, let me know if you have any further queries.