ASPNETCORE_Environment overrides cmd parameter

Describe the bug

We’ve noticed a very strange behavior of hosting environment setting. When using ASPNETCORE_Environment="fromEnv" environment variable and --Environment=fromCmd command-line argument then for some reason the environment variable wins.

This is very inconsistent given that:

1. ASPNETCORE_urls vs --urls - command-line argument wins 📗
2. DOTNET_ENVIRONMENT vs --Environment - command-line argument wins 📗
3. ASPNETCORE_ENVIRONMENT vs --Environment - environment variable wins 📙

To Reproduce

1. (This one works well) When I don’t set any environment variables, the command-line argument is applied:

dotnet .\WebApplication_TestEnvironment.dll --Environment=fromCmd
Current environment: fromCmd

1. (This one works well too) When I set DOTNET_ENVIRONMENT environment variable, the command-line argument wins:

$ENV:DOTNET_ENVIRONMENT="fromDotnetEnv"
dotnet .\WebApplication_TestEnvironment.dll --Environment=fromCmd
Current environment: fromCmd

1. (This one doesn’t work) When I set ASPNETCORE_ENVIRONMENT environment variable, then hosting environment is defined by the environment variable and not by cmd:

$ENV:ASPNETCORE_ENVIRONMENT="fromAspEnv"
dotnet .\WebApplication_TestEnvironment.dll --Environment=fromCmd
Current environment: fromAspEnv

I am able to reproduce it on a newly created ASP.NET Core 3.1 API project. The only small change I did is writing the current environment to the Console .

    public class Program
    {
        public static void Main(string[] args)
        {
            CreateHostBuilder(args).Build().Run();
        }

        public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseStartup<Startup>();
                });
    }

   ....................................................................

    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllers();
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            Console.WriteLine($"Current environment: {env.EnvironmentName}");

            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });
        }
    }

Further technical details

dotnet --info
.NET Core SDK (reflecting any global.json):
 Version:   3.1.100
 Commit:    cd82f021f4

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.18362
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\3.1.100\

Host (useful for support):
  Version: 3.1.0
  Commit:  65f04fb6db

.NET Core SDKs installed:
  1.1.9 [C:\Program Files\dotnet\sdk]
  2.1.201 [C:\Program Files\dotnet\sdk]
  2.1.508 [C:\Program Files\dotnet\sdk]
  2.1.509 [C:\Program Files\dotnet\sdk]
  2.1.701 [C:\Program Files\dotnet\sdk]
  2.1.801 [C:\Program Files\dotnet\sdk]
  2.2.109 [C:\Program Files\dotnet\sdk]
  2.2.401 [C:\Program Files\dotnet\sdk]
  3.1.100 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.14 [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 2.2.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.14 [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 2.2.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 1.0.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 1.1.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.7 [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 2.1.13 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.14 [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 2.2.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

[KoshelevS]

Any news on this?

I’ve created the following extension method as a workaround, but it has not been battle-tested yet

        public static IWebHostBuilder FixEnvironmentParam(this IWebHostBuilder webBuilder, string[] args)
        {
            var configBuilder = new ConfigurationBuilder();
            configBuilder.AddCommandLine(args);
            var config = configBuilder.Build();

            var env = config[HostDefaults.EnvironmentKey];
            if (string.IsNullOrWhiteSpace(env))
            {
                return webBuilder;
            }

            return webBuilder.ConfigureAppConfiguration((host, _) => host.HostingEnvironment.EnvironmentName = env)
                             .UseEnvironment(env);
        }

[adityamandaleeka]

Triage: this seems low priority and the current behavior is now documented better. Closing this issue.