How to set hosting environment for a specific website?

My site is running under IIS among a dozen others. I want to set its hosting environment to Staging, but I can't use ASPNETCORE_ENVIRONMENT environment variable to set it, because of the aforementioned other sites.

How can I set the hosting environment for a specific site.

P.S. Found the documentation that addresses this specific scenario. The short story is change web.config (yes, the legacy file).

While it is not easy to find, but when Microsoft documented ASP.NET Core module they did provide sample code on how to set environment variables in web.config, so there is no need to follow the other answer to modify applicationHost.config.

<aspNetCore processPath="dotnet"
      arguments=".\MyApp.dll"
      stdoutLogEnabled="false"
      stdoutLogFile=".\logs\stdout"
      hostingModel="inprocess">
  <environmentVariables>
    <environmentVariable name="ASPNETCORE_ENVIRONMENT" value="Development" />
    <environmentVariable name="CONFIG_DIR" value="f:\application_config" />
  </environmentVariables>
</aspNetCore>

It is the same web.config generated by dotnet publish, so I believe you feel natural that further changes go to the same place.

Another way you might want is to configure such environment variables on the application pool.

You can override ASPNETCORE_ENVIRONMENT for the single site inside IIS without changing and redeploying your app.

1. Open IIS Manager
2. Select the website for which you want to set the hosting environment
3. Click on the "Configuration Editor" feature
4. In the the "Configuration Editor" select system.webServer/aspNetCore in the dropdown and just to the right og this, REMEMBER to select ApplicationHost.config. If you fotget, you will set this variable in the used web.config for the running site. Then ofcause it will be overwritten when you deploy a new version of the website. The ApplicationHost.config sets it machine level, so the setting will live in a deffenrent place.
5. Mark environmentVariables line and click the tree dots at the end to edit the list.
6. Click the Add button and set the name to ASPNETCORE_ENVIRONMENT and value to Staging
7. Restart the website for the changes to take effect.

Also you can set environment from code or configuration via UseEnvironment method. Note that you need to redeploy an application to apply this changes:

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

    public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
        WebHost.CreateDefaultBuilder(args)
            .UseEnvironment("Staging");
}