React and ASP.NET Core - deployment not publishng SPA

I have created an out of the box react app with ASP.NET Core Web API (.NET 9, VS 2022 17.13.5).

In former versions (.NET 6), I'd get a ClientApp nested in the backend solution, and when I publish - this is all included.

Now I have:

• MyApp.Server
• myapp.client

When I publish MyApp.Server, the backend application is deployed, but the frontend is not.

Local (folder) or server logs shows the following warning:

warn: Microsoft.AspNetCore.StaticFiles.StaticFileMiddleware[16]
The WebRootPath was not found: ..
\MyApp.Server\bin\Release\net9.0\publish\wwwroot. Static files may be unavailable.

But that can be expected as the website isn't there.

Has anyone had a similar issue? .NET 6 worked out of the box.

Any help greatly appreciated,
David

We need to add below settings to put the react publish files under wwwroot folder.

And as we know, app.MapStaticAssets(); is used for .NET9, and app.UseStaticFiles(); still works. There is official documentation about the difference MapStaticAssets and UseStaticFiles, I know it very well, but in this case we need to use app.UseStaticFiles(); to solve the 404 problem.

Here is my all changes in my brand new project.

project_name.Server.csproj.

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>net9.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
    <SpaRoot>..\react_spa.client</SpaRoot>
    <SpaProxyLaunchCommand>npm run dev</SpaProxyLaunchCommand>
    <SpaProxyServerUrl>https://localhost:51035</SpaProxyServerUrl>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="9.0.2" />
    <PackageReference Include="Microsoft.AspNetCore.SpaProxy">
      <Version>9.*-*</Version>
    </PackageReference>
  </ItemGroup>

  <ItemGroup>
    <ProjectReference Include="..\react_spa.client\react_spa.client.esproj">
      <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
    </ProjectReference>
  </ItemGroup>
  <!--Please add below settings, it can build the react project and save it under wwwroot folder-->
    
  <Target Name="DebugEnsureNodeEnv" BeforeTargets="Build">
    <Exec Command="node --version" ContinueOnError="true">
      <Output TaskParameter="ExitCode" PropertyName="ErrorCode" />
    </Exec>
    <Error Condition="'$(ErrorCode)' != '0'" Text="Node.js is required to build this project." />
  </Target>
  
  <Target Name="PublishReact" AfterTargets="ComputeFilesToPublish">
    
    <Exec WorkingDirectory="$(SpaRoot)" Command="npm install" />
    
    <Exec WorkingDirectory="$(SpaRoot)" Command="npm run build " />
  
    <ItemGroup>
      <DistFiles Include="$(SpaRoot)\dist\**" />
      <ResolvedFileToPublish Include="@(DistFiles->'%(FullPath)')" Exclude="@(ResolvedFileToPublish)">
        <RelativePath>wwwroot\%(RecursiveDir)%(FileName)%(Extension)</RelativePath>
        <CopyToPublishDirectory>PreserveNewest</CopyToPublishDirectory>
      <ExcludeFromSingleFile>true</ExcludeFromSingleFile>
      </ResolvedFileToPublish>
    </ItemGroup>
  </Target>

</Project>

Program.cs

var app = builder.Build();

app.UseDefaultFiles();
//app.MapStaticAssets();
app.UseStaticFiles();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.MapOpenApi();
}

app.UseHttpsRedirection();

app.UseAuthorization();

app.MapControllers();

app.MapFallbackToFile("/index.html");

app.Run();

Test Result