Blazor WASM not loading appsettings.{environment}.json in Azure App Services

[hallidev]

Describe the bug

When developing locally (Blazor WASM), I have the following files in /wwwroot:

appsettings.json
appsettings.Development.json
appsettings.LocalDevelopment.json

My launchSettings.json specifies an ASPNETCORE_ENVIRONMENT of "LocalDevelopment".

When running locally, everything works as expected. appsettings.json and appsettings.LocalDevelopment.json are merged as expected.

I have just published the Blazor WASM app to Azure App Services, and appsettings.json merging fails. I have the ASPNETCORE_ENVIRONMENT set to "Development" in the App Service:

I have been able to confirm the failure by putting all of my settings in appsettings.json so that I don't need to rely on merging. The app runs as expected in the App Service.

To Reproduce

1: Create a new Blazor WASM ASP.NET Core Hosted application
2: Add appsettings.json, and appsettings.Development.json to /wwwroot
3: Add a configuration value to both files that requires merging.
4: Locally, set ASPNETCORE_ENVIRONMENT to "Development"
5: Confirm that the correct config value gets read
6: Deploy to Azure App Service
7: Set ASPNETCORE_ENVIRONMENT to "Development" for the App Service
8: BUG: Note that value is not read from appsettings.Development.json. It is read from appsettings.json.

Further technical details

• ASP.NET Core version 3.1
• Include the output of dotnet --info

.NET Core SDK (reflecting any global.json):
 Version:   3.1.401
 Commit:    5b6f5e5005

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.19041
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\3.1.401\

Host (useful for support):
  Version: 3.1.7
  Commit:  fcfdef8d6b

.NET Core SDKs installed:
  2.1.700 [C:\Program Files\dotnet\sdk]
  2.1.701 [C:\Program Files\dotnet\sdk]
  2.1.801 [C:\Program Files\dotnet\sdk]
  2.2.300 [C:\Program Files\dotnet\sdk]
  2.2.301 [C:\Program Files\dotnet\sdk]
  2.2.401 [C:\Program Files\dotnet\sdk]
  3.0.100 [C:\Program Files\dotnet\sdk]
  3.1.101 [C:\Program Files\dotnet\sdk]
  3.1.401 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.21 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.2.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.2.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.21 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.2.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.2.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.21 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.0.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.1.1 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.1.7 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

• The IDE (VS / VS Code/ VS4Mac) you're running on, and it's version - Visual Studio 2019 v16.7.2

[mkArtakMSFT]

Thanks for contacting us. This may be potentially related to another reported issue: #21992

Thanks for contacting us.
We're moving this issue to the Next sprint planning milestone for future evaluation / consideration. We will evaluate the request when we are planning the work for the next milestone. To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[hallidev]

@mkArtakMSFT

I'm curious why this is considered minor severity and has been pushed from Next sprint planning? This is a pretty major issue and a deviation from how everything else in the .NET Core ecosystem works. It also makes managing configuration across environments very difficult. We have to manually edit appSettings.json to match the environment we're about to deploy to every single time we need to do a deployment.

I'm surprised that this issue hasn't been reported frequently. Am I missing something?

[trygvelo]

We solved it like this:

1. In Visual Studio project properties -> "Build Event" -> "Pre-build event command line", add the following line:
   echo window.BlazorEnvironment = '$(ConfigurationName)'; > $(ProjectDir)wwwroot\js\BlazorEnvironment.js

2. In index.html, BEFORE bootstrapping Blazor with this tag: <script src="_framework/blazor.webassembly.js"></script>, add the following to make sure the "blazor-environment" header is set to the correct value:

<script src="js/BlazorEnvironment.js"></script>
<script>
    const originalFetch = fetch;
    fetch = async (url, options) => {
        const response = await originalFetch(url, options);
        return url.endsWith('/blazor.boot.json')
            ? new Response(await response.blob(), { headers: { 'blazor-environment': window.BlazorEnvironment } })
            : response;
    };
</script>

[hallidev]

@trygvelo Thanks - will give this a try