.NET6 isolated function on Windows fails

This turned out to be an issues with indirectly referenced old packages, configuration, and the publishing profile, all of which were only discoverable in the Kudu logs. The issue can be considered resolved, but some information from the team about if or how the issue could’ve been seen in the portal would be very helpful for future readers.

Issue 1: It was not possible to find any compatible framework version This was caused by Visual Studio’s default publishing profile having a Deployment mode setting of Framework-dependent.

Resolution Changing the deployment mode in the publishing profile to Self-contained

Issue 2: Did not find any initialized language workers This ended up being a combination of two things:

• a configuration setting was missing that instructed the AzureServiceTokenProvider to use the user-assigned identity
• the Azure Key Vault configuration extension package Microsoft.Extensions.Configuration.AzureKeyVault pulled in an older version of Microsoft.Azure.Services.AppAuthentication (1.0.3) which did not support the documented connection string.

Resolution Adding the configuration string and then explicitly (rather than indirectly) referencing the most recent version of Microsoft.Azure.Services.AppAuthentication

There is a newer library for Key Vault integration but we haven’t had time to investigate usage at this time, or compatibility with functions.

repro.zip

Repro instructions

1. Download and unzip the attached respro code.

2. Create a function app with the following settings:

   • net6.0
   • v4
   • dotnet-isolated
   • windows

3. Create a user managed identity and assign it to the function. The function should not have a system assigned identity enabled, only the user managed identity.

4. Create a new key vault instance with RBAC-based access control.

5. Assign the user identity from step 3 using the Key Vault Reader role.

6. In the Program.cs, replace the AppId in the string on L28 with the Client Id from the user managed identity in step 3.

7. On line 32, replace the first parameter with the URL of the key vault created in step 5.

8. Publish the function to the function app using the following settings (I did this from Visual Studio 2022):

   • Configuration: Release|AnyCPU
   • Target framework: net6.0
   • Deployment mode: Framework-dependent
   • Target runtime: win-x64

9. Once the function starts up, it should start failing immediately. In Application Insights, System.InvalidOperation exceptions should start showing up with the message Exception while executing function: Functions.Repro Did not find any initialized language workers

10. Going to the Kudu debug console and navigating to the logs under C:\home\LogFiles\Application\Functions\Host will show the error:

    2022-04-13T19:54:21.318 [Information] The framework 'Microsoft.NETCore.App', version '6.0.4' (x64) was not found.
    2022-04-13T19:54:21.318 [Information] - The following frameworks were found:
    2022-04-13T19:54:21.318 [Information] 2.2.14 at [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
    2022-04-13T19:54:21.318 [Information] 3.0.3 at [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
    2022-04-13T19:54:21.318 [Information] 3.1.18 at [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
    2022-04-13T19:54:21.319 [Information] 3.1.23 at [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
    2022-04-13T19:54:21.319 [Information] 5.0.14 at [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
    2022-04-13T19:54:21.319 [Information] 5.0.15 at [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
    2022-04-13T19:54:21.319 [Information] 6.0.2 at [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
    2022-04-13T19:54:21.319 [Information] 6.0.3 at [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
    

    Observation: The framework error only started appearing once I added the key vault extensions nuget package. Prior to that, the function actually ran as expected.

11. From the publish profile, change the Deployment mode setting to Self-contained and republish the function.

12. Identical errors will appear in Application Insights as in step 10.

13. Again going to the logs from the Kudu debug console, the error changes to:

    2022-04-13T20:04:25.536 [Information] Unhandled exception. System.ArgumentException: Connection string RunAs=App;AppId=REDACTED is not valid. Must contain 'TenantId' attribute and it must not be empty.
    2022-04-13T20:04:25.537 [Information] at Microsoft.Azure.Services.AppAuthentication.AzureServiceTokenProviderFactory.ValidateAttribute(Dictionary`2 connectionSettings, String attribute, String connectionString)
    2022-04-13T20:04:25.538 [Information] at Microsoft.Azure.Services.AppAuthentication.AzureServiceTokenProviderFactory.Create(String connectionString, String azureAdInstance)
    2022-04-13T20:04:25.538 [Information] at Microsoft.Azure.Services.AppAuthentication.AzureServiceTokenProvider..ctor(String connectionString, String azureAdInstance)
    2022-04-13T20:04:25.538 [Information] at NoLanguageRepro.Program.<>c.<Main>b__0_0(HostBuilderContext _, IConfigurationBuilder c) in C:\Users\REDACTEDMYUSERNAME\Documents\Visual Studio 2022\Projects\NoLanguageRepro\NoLanguageRepro\Program.cs:line 28
    2022-04-13T20:04:25.538 [Information] at Microsoft.Extensions.Hosting.HostBuilder.BuildAppConfiguration()
    2022-04-13T20:04:25.538 [Information] at Microsoft.Extensions.Hosting.HostBuilder.Build()
    2022-04-13T20:04:25.539 [Information] at NoLanguageRepro.Program.Main() in C:\Users\mwan\Documents\Visual Studio 2022\Projects\NoLanguageRepro\NoLanguageRepro\Program.cs:line 23