The Azure App Service returned HTTP Error 500.31 - ANCM Failed to Find Native Dependencies

Xu, Ni 0 Reputation points
2026-08-17T02:47:59.8066667+00:00

The Azure App Service returned HTTP Error 500.31 - ANCM Failed to Find Native Dependencies after I build and deploy steps succeeded. The background is I use develop pipelines DotNetCoreCLI@2 to update the project to .net 11 preview 6, is it because the Azure Window App service does not support to preinstall .NET 11 preview runtimes?

Azure App Service
Azure App Service

Azure App Service is a service used to create and deploy scalable, mission-critical web apps.

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  1. AI answer

    2026-08-17T02:48:16.4466667+00:00

    Yes. That is a likely cause.

    Azure App Service doesn’t deploy ASP.NET Core preview releases by default. A 500.31 startup failure commonly occurs when the required Microsoft.NETCore.App or Microsoft.AspNetCore.App runtime isn’t installed on the target machine. If the app was updated in the pipeline to target .NET 11 preview 6, the App Service instance can fail at startup if that preview runtime isn’t available there.

    Relevant checks and fixes:

    1. Confirm the app is targeting a preview runtime.
      • Check the app’s .runtimeconfig.json or project target/runtime settings.
      • If it requests a preview Microsoft.AspNetCore.App version, that matches the documented 500.31/handler load failure pattern when the framework version isn’t present.
    2. If the app must run on a preview runtime, install the matching preview site extension.
      • For preview runtimes on Azure App Service, install only one site extension that matches the app bitness: x86 or x64.
      • Do not install both x86 and x64 preview runtime site extensions.
      • After installing or removing the incorrect one, restart the app and wait a few seconds.
    3. Verify process architecture matches the deployed app.
      • If the app is x64, use the x64 preview runtime extension and ensure the App Service process bitness matches.
      • Architecture mismatch can also cause startup failures.
    4. If preview runtime support is not required, use a supported installed runtime instead.
      • Retarget the app to a .NET version available on App Service.
      • Or publish as a self-contained deployment so the app carries its own runtime.
    5. Collect startup diagnostics to confirm.
      • Check Application Event Log entries.
      • Check ASP.NET Core Module stdout/debug logs.
      • These logs typically show the missing framework/version that the app requested.

    If the deployment succeeded but the site fails only at runtime, that strongly points to runtime availability on App Service rather than a pipeline build problem.

    References:

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