View is not found when a Web App is deployed with Azure DevOps

Question

I just migrated my Asp.Net MVC web application from .Net 2.2 to 8.0. I built and deployed the application as a Web App on Azure DevOps. When I tried to run the application in a browser, I get HTTP Error 500.0 - Internal Server Error.

I tried to diagnose using Application Insights, and found an exception:

The view 'Index' was not found. The following locations were searched:

/Views/Home/Index.cshtml
/Views/Shared/Index.cshtml
/Pages/Shared/Index.cshtml

I don't understand what could cause this, as the file is present in my project, and it runs successfully on my local computer from Visual Studio.

ADDED:

My application uses Startup.cs.

Before migration, it has the following code:

        app.UseMvc(routes =>
        {
            routes.MapRoute(
                name: "default",
                template: "{controller=Home}/{action=Index}/{id?}");
        });

It was replaced with this:

        app.UseRouting();
        ...
        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllerRoute(
                name: "default",
                pattern: "{controller=Home}/{action=Index}/{id?}");
            endpoints.MapRazorPages();
        });

And here is my Azure pipeline:

variables:
- name: BuildParameters.RestoreBuildProjects
  value: '**/*.csproj'
trigger:
  branches:
    include:
    - refs/heads/master
name: $(date:yyyyMMdd)$(rev:.r)
jobs:
- job: Job_1
  displayName: Agent job 1
  pool:
    vmImage: windows-latest
  steps:
  - checkout: self
  - task: UseDotNet@2
    displayName: Use .NET Core sdk 8.0.x
    inputs:
      version: 8.0.x
  - task: DotNetCoreCLI@2
    displayName: Restore
    inputs:
      command: restore
      projects: $(BuildParameters.RestoreBuildProjects)
      feedRestore: a1dd11ff-23bd-23dd-9782-e9876d2569db
  - task: DotNetCoreCLI@2
    displayName: Build
    inputs:
      projects: $(BuildParameters.RestoreBuildProjects)
      arguments: --configuration $(BuildConfiguration)
  - task: DotNetCoreCLI@2
    displayName: Publish
    inputs:
      command: publish
      publishWebProjects: True
      projects: $(BuildParameters.RestoreBuildProjects)
      arguments: --configuration $(BuildConfiguration) --output 
$(build.artifactstagingdirectory)
      zipAfterPublish: True
  - task: PublishBuildArtifacts@1
    displayName: Publish Artifact
    condition: succeededOrFailed()
    inputs:
      PathtoPublish: $(build.artifactstagingdirectory)
      TargetPath:   '\\my\share\$(Build.DefinitionName)\$(Build.BuildNumber)'

And here is my folder structure:

ADDED:

I downloaded the artifacts and copied them into the bin/Debug/net8.0 folder on my computer, and then ran from Visual Studio. The application worked as expected. Then I tried to run it without Visual Studio, from the executable directly. This time it got me the same error, as on Azure:

warn: Microsoft.AspNetCore.HttpsPolicy.HttpsRedirectionMiddleware[3]
  Failed to determine the https port for redirect.
fail: Microsoft.AspNetCore.Mvc.ViewFeatures.ViewResultExecutor[3]
  The view 'Index' was not found. Searched locations: /Views/Home/Index.cshtml, /Views/Shared/Index.cshtml, /Pages/Shared/Index.cshtml
fail: Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware[1]
  An unhandled exception has occurred while executing the request.
  System.InvalidOperationException: The view 'Index' was not found. The following locations were searched:
  /Views/Home/Index.cshtml
  /Views/Shared/Index.cshtml
  /Pages/Shared/Index.cshtml
     at Microsoft.AspNetCore.Mvc.ViewEngines.ViewEngineResult.EnsureSuccessful(IEnumerable`1 originalLocations)
     at Microsoft.AspNetCore.Mvc.ViewFeatures.ViewResultExecutor.ExecuteAsync(ActionContext context, ViewResult result)
     at Microsoft.AspNetCore.Mvc.ViewResult.ExecuteResultAsync(ActionContext context)
     at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeResultAsync>g__Logged|22_0(ResourceInvoker invoker, IActionResult result)
     at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResultFilterAsync>g__Awaited|30_0[TFilter,TFilterAsync](ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
     at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResultExecutedContextSealed context)
     at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.ResultNext[TFilter,TFilterAsync](State& next, Scope& scope, Object& state, Boolean& isCompleted)
     at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeResultFilters()
  --- End of stack trace from previous location ---
     at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|25_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
     at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context)
     at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
     at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeFilterPipelineAsync()
  --- End of stack trace from previous location ---
     at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Logged|17_1(ResourceInvoker invoker)
     at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Logged|17_1(ResourceInvoker invoker)
     at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
     at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
     at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
     at Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddlewareImpl.<Invoke>g__Awaited|10_0(ExceptionHandlerMiddlewareImpl middleware, HttpContext context, Task task)
fail: Microsoft.AspNetCore.Mvc.ViewFeatures.ViewResultExecutor[3]
  The view 'Error' was not found. Searched locations: /Views/Home/Error.cshtml, /Views/Shared/Error.cshtml, /Pages/Shared/Error.cshtml
fail: Microsoft.AspNetCore.Diagnostics.ExceptionHandlerMiddleware[3]
  An exception was thrown attempting to execute the error handler.
  System.InvalidOperationException: The view 'Error' was not found. The following locations were searched:
  /Views/Home/Error.cshtml
  /Views/Shared/Error.cshtml
  /Pages/Shared/Error.cshtml

Answer 1

The template project we create will include all the view pages by default when you publish it.

In addition, from the comparison in the image below, we can see that from .NET Core 2.0+ and .NET 8 release files, .NET 8 has removed the projectname. Views.dll. That's why we forced the Views folder to be included during the publishing process when we first troubleshoot.

Workaround

Using below settings in your .csproj, it can fix the issue.

  <ItemGroup>
    <ViewFiles Include="$(ProjectDir)\Views\**\*.cshtml" />
  </ItemGroup>
  
  <Target Name="CopyViewFilesAfterPublish" AfterTargets="Publish">
    <Copy SourceFiles="@(ViewFiles)"
      DestinationFolder="$(PublishDir)\Views\%(RecursiveDir)"
    />
  </Target>
  <ItemGroup>
    <ViewFiles Include="$(ProjectDir)\Areas\**\*.cshtml" />
  </ItemGroup>
  
  <Target Name="CopyViewFilesAfterPublish" AfterTargets="Publish">
    <Copy SourceFiles="@(ViewFiles)"
      DestinationFolder="$(PublishDir)\Areas\%(RecursiveDir)"
    />
  </Target>

Soultion

<ItemGroup>
    <Content Include="Views\**">
    <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
    </Content>
</ItemGroup>

For more details, you can check below 2 threads.

This solution will keep your publishing files clean and won't generate redundant Views and Areas folders, but you may need to learn MSBuild-related documentation.

1. Can't find my repo files after deploying to Azure App Service

2. How to add a folder and its contents with build action content in to uwp project?