How to set hosting environment name for .NET Core console app using Generic Host (HostBuilder)

Question

I am setting up a .NET Core 2.x console app as a Windows service and need to load an appsettings json file based on the environment. I was thinking to start the service with a command line argument that identifies the environment. How can I do that in Visual Studio? No matter what I set in the project settings, the EnvironmentName value is always "Production".

How can I set my environment from a command line argument?

var hostBuilder = new HostBuilder()
                 .UseContentRoot(Directory.GetCurrentDirectory())
                 .ConfigureAppConfiguration((hostingContext, config) =>
                 {
                     var env = hostingContext.HostingEnvironment;
                     config.AddCommandLine(args);
                     config.AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: false, reloadOnChange: true);
                     config.AddEnvironmentVariables();
                 })
                 .ConfigureServices((hostContext, services) =>
                 {
                     //Inject additional services as needed
                     services.AddHostedService<JobRunner>();
                });

Answer 1

You can set the environment from the command line variables via the ConfigureHostConfiguration extension method.

Set up the configuration for the builder itself. This will be used to initialize the Microsoft.Extensions.Hosting.IHostEnvironment for use later in the build process.

var hostBuilder = new HostBuilder()
    .UseContentRoot(Directory.GetCurrentDirectory())
    .ConfigureHostConfiguration(configurationBuilder => {
        configurationBuilder.AddCommandLine(args);
    })
    .ConfigureAppConfiguration((hostingContext, cfg) =>
    {
        // ...

        var env = hostingContext.HostingEnvironment;
        Console.WriteLine(env.EnvironmentName); // Test
        // ...
    });
    
    // ...

    hostBuilder.Build();

---

In Visual Studio, you configure the application arguments with the same ones as being used by dotnet run which is --environment,
e.g. dotnet run --environment Test.

Without this application argument, the hosting environment defaults back to Production.

Answer 2

In Visual Studio, you can add an environment variable under the Debug tab of the console application properties. For a console application the environment variable provider name must be prefixed by DOTNET_ for the generic host builder to recognize it. In this case, the provider name is DOTNET_ENVIRONMENT.

If this provider name is not specified, the default is Production.

Reference : https://learn.microsoft.com/en-us/aspnet/core/fundamentals/host/generic-host?view=aspnetcore-5.0#host-configuration

Answer 3

Another method is to use the "UseEnvironnement" method directly on the host builder :

https://learn.microsoft.com/en-us/dotnet/api/microsoft.extensions.hosting.hostinghostbuilderextensions.useenvironment?view=dotnet-plat-ext-5.0

For example :

   public static IHostBuilder CreateHostBuilder(string[] args) =>
            Host.CreateDefaultBuilder(args)
                .UseEnvironment("dev") // Magic is here
                .ConfigureWebHostDefaults(webBuilder =>
                {
                    webBuilder.UseUrls("http://0.0.0.0:8081");
                    webBuilder.UseStartup<Startup>();
                });