App startup fails on F1 and D1 instances, but works on B1, S1 and above?

Question

Code runs fine locally in debug and release mode. Deployed to an S1 or B1 App Service it also runs fine. Recently, without any code changes, my D1 App Service stopped working out of the blue. When I try to access the site, I get a 502.5 ANCM Out-Of-Process Startup Failure.

So I enabled stdout and got the following log...

System.InvalidOperationException: Unable to resolve service for type 'Microsoft.AspNetCore.Identity.IUserStore\1[XXXXX.Domain.Authentication.ApplicationUser]' while attempting to activate 'Microsoft.AspNetCore.Identity.UserManager`1[XXXXX.Domain.Authentication.ApplicationUser]'.`

Like I said, nothing changed with the code or my Azure App Service in the past 2 months, however, this started happening two days ago. Why would I just now start receiving this error and why does it work on an S1? Also, I've looked at metrics and my quotas are nowhere close to being hit. The site has an average of between 2-8 users a day.

Answer 1

Thanks for asking question! The cause of a process startup failure can usually be determined from entries in the Application Event Log and the ASP.NET Core Module stdout log. For accessing the Application Event Log you may use the Diagnose and solve problems blade in the Azure portal:

Sign in Azure portal> App Services >Select Diagnose and solve problems> Select Diagnostic Tools > Support Tools, select the Application Events button> Examine the latest error provided by the IIS AspNetCoreModule or IIS AspNetCoreModule V2 entry in the Source column.

You may also refer to Additional troubleshooting methods : https://learn.microsoft.com/en-us/aspnet/core/test/troubleshoot-azure-iis?view=aspnetcore-2.2#troubleshoot-on-azure-app-service

Let me know if issue persists