Visual Studio Net Core: Switch Environment Variables for Multiple Projects

One way to solve this is to have a solution-level "environment" text file, that each API project can "link" to. Then in each API project's Program or Startup logic, have them read this global file to set the environment at run time.

As an example, here's my sample solution which has 2 API projects in it:

Step 1: Create The 'Global' Environment File

Firstly, I added a solution-level text file Environment.txt that simply has the name of the 'current' environment I wish to run all my API's under:

Performance

Step 2: Link The Environment.txt File To Each API Project

Second is linking the Environment.txt file to each API project, using Visual Studio's Add Existing Item dialog, and choosing the Add As Link option:

Notice that the icon on linked files is slightly different than a normal file.

Step 3: Ensure Environment.txt Actually Gets Copied To The Bin Directory(s)

Thirdly is ensuring that each of the added linked file's Copy to Output option is set to Copy Always:

Step 4: A Small Bit Of Code...

And finally, in each API project's Program.cs file, you can read this file and set the environment at run-time:

namespace MicroserviceSandbox.ApiTwo{    using System.IO;    using Microsoft.AspNetCore.Hosting;    using Microsoft.Extensions.Hosting;    public class Program    {        public static void Main(string[] args)        {            CreateHostBuilder(args).Build().Run();        }        public static IHostBuilder CreateHostBuilder(string[] args)        {            return Host.CreateDefaultBuilder(args)                .ConfigureWebHostDefaults(webBuilder =>                {                    // *** Dynamically set the environment.                    var binDirectoryPath = new FileInfo(typeof(Program).Assembly.Location).Directory.FullName;                    var environmentFilePath = Path.Combine(binDirectoryPath, "Environment.txt");                    var environment = File.ReadAllText(environmentFilePath);                    webBuilder.UseEnvironment(environment);                    // ***                    webBuilder.UseStartup<Startup>();                });        }    }}

Assumptions

• The above C# code snippet assumes your API projects are using ASP.NET Core v3.1.

Instead of using the environment variables from the project launchsettings, you can also use the system environment variables.

To do so, you have to remove the "ASPNETCORE_ENVIRONMENT" from the launchsettings and set in system enviroment variables.See docu here: https://docs.microsoft.com/en-us/aspnet/core/fundamentals/environments?view=aspnetcore-3.1#set-the-environment

Caution: Every project on the same machinge not having the "ASPNETCORE_ENVIRONMENT" set in the launchsetting will use the system enviroment variable

As shown on your screenshot, the "app environment" is determined by that "windows process environment variable". Only the project that is being run needs to set that environment variable, not the projects refenced by that one.

If you are running multiple projects at the same time:The environment variable is saved to the launchSettings.json file in the project folder. You could us a PowerShell script to update the launchSettings of many projects at once.