ASP.NET Core hosting environment variable ignored
I just spent the last couple hours dealing with the same issue. I'm not sure if the result will be the same since you seem to have one of two applications working.
I set the ASPNETCORE_ENVIRONMENT to "Staging" as a system variable through "Advanced System Settings" on Windows Server 2008 R2 and always ended up in the "Production" environment (which is the default environment if it can't find the setting anywhere).
Using "set" from Command Prompt showed the expected results of "ASPNETCORE_ENVIRONMENT=Staging".
Calling Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") returned null. I created another variable called "Test" which also returned null. Calling any other existing variable returned expected results.
I tried recycling the application pool, changing the app pool's user, restarting IIS through management console, even restarting World Wide Web Publishing Service (probably same as reset in IIS mgmt console) all to no avail.
Rebooting the server was the only way I could get the application to return the expected result.
As said in this similar question, the trick was simply to set the app pool to load the user variables (IIS -> Server -> App Pools -> Right click on pool -> Set application pool defaults... -> Load User Profile = True).
I configured only one of my app pools accordingly, thus only one of the sites could access the environment variables.
From a cmd window, run
net stop /y was && net start w3svc.
Source: ASP.NET Core Docs -> Use multiple environments in ASP.NET Core
Note: Restarting IIS via right click-> stop -> start in IIS Manager will NOT work.
If you are debugging your code in Visual Studio, bear in mind that Visual Studio caches the environment variables that were present when Visual Studio was started - not when you hit "debug"!
So you may have to restart Visual Studio for any changes to the environment to be visible.