After RC2

So what is the way to set a different EnvironmentName?

Set the ASPNETCORE_ENVIRONMENT environmental variable.

There are many ways to set that environmental variable. These include a launchSettings.json profile and other environment-specific ways. Here are some examples.

From a console:

// PowerShell
> $env:ASPNETCORE_ENVIRONMENT="Development"

// Windows Command Line
> SET ASPNETCORE_ENVIRONMENT=Development

// Bash
> ASPNETCORE_ENVIRONMENT=Development

From an Azure Web App’s App settings:

Before RC2

I can imagine that it should be set in “Commands” as a parameter for server.

That is true. In your project.json, add --ASPNET_ENV production as a parameter for the server.

"commands": {
  "web": "Microsoft.AspNet.Hosting --ASPNET_ENV production --server Microsoft.AspNet.Server.WebListener --server.urls http://localhost:5001"
}

Now when you run dnx . web from the command line, ASPNET_ENV will be production.

Relevant ASP.NET Core Hosting Source Code

The WebHostBuilder combines "ASPNETCORE_" with the WebHostDefaults.EnvironmentKey to make "ASPNETCORE_environment". It also supports the legacy keys.

WebHostDefaults.cs

namespace Microsoft.AspNetCore.Hosting
{
    public static class WebHostDefaults
    {
        public static readonly string ApplicationKey = "applicationName";
        public static readonly string StartupAssemblyKey = "startupAssembly";

        public static readonly string DetailedErrorsKey = "detailedErrors";
        public static readonly string EnvironmentKey = "environment";
        public static readonly string WebRootKey = "webroot";
        public static readonly string CaptureStartupErrorsKey = "captureStartupErrors";
        public static readonly string ServerUrlsKey = "urls";
        public static readonly string ContentRootKey = "contentRoot";
    }
}

WebHostBuilder.cs

_config = new ConfigurationBuilder()
    .AddEnvironmentVariables(prefix: "ASPNETCORE_")
    .Build();

if (string.IsNullOrEmpty(GetSetting(WebHostDefaults.EnvironmentKey)))
{
    // Try adding legacy environment keys, never remove these.
    UseSetting(WebHostDefaults.EnvironmentKey, 
        Environment.GetEnvironmentVariable("Hosting:Environment") 
        ?? Environment.GetEnvironmentVariable("ASPNET_ENV"));
}

Backward Compatibility

The environment key is set with the ASPNETCORE_ENVIRONMENT environment variable. ASPNET_ENV and Hosting:Environment are still supported, but generate a deprecated message warning.

https://docs.asp.net/en/latest/migration/rc1-to-rtm.html

Default Value

The default value is “Production” and is set here.