APP_POOL_ID environment variable is null when Preload = True

[NinjaCross]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

As highlighted here #47093 (comment), when running an ASP.NET CORE application (.NET 6 and higher) in IIS with "Preload = true" (Application Initialization module), the APP_POOL_ID environment variable is null.

Setting "Preload = false" in IIS everything works fine, the APP_POOL_ID environment variable is correctly set.

This is a significant problem in some scenarios, because the application is not aware of its Application Pool, which is often a discriminator for configurations loading.

In my case, for example, multiple Application Pools and WebSites are sharing/based on the same application folder and files (every web site loads its own configuration based on the name of the Application Pool that hosts it)

I tried waiting for the variable to be populated (since the original post seemed to suggest that this problem is somehow time-related), but it never happens.

var appPoolId = Environment.GetEnvironmentVariable("APP_POOL_ID");
logger.LogInformation("App Pool Id = {AppPoolId}", appPoolId);

if (string.IsNullOrWhiteSpace(appPoolId))
{          
        do
        {
            logger.LogError("App Pool Id is NOT VALID. This is NOT allowed in {EnvironmentName}", appBuilder.Environment.EnvironmentName);
            appPoolId = Environment.GetEnvironmentVariable("APP_POOL_ID");

            if (string.IsNullOrWhiteSpace(appPoolId)) // still unresolved ?
            {
                // wait a bit, maybe the environment variables will be set correctly
                Thread.Sleep(1000);
            }
            else
            {
                break; // App Pool ID resolved, exit the loop and continue with the application initialization
            }

        } while (true); // loop unti a valid App Pool Id is resolved
}

I also couldn't find any documentation about this behaviour, or anything related.
Is it a bug in IIS ? In ASP.NET CORE ?
Is there a known workaround, or a proper solution to this problem ?

Any suggestion will be greatly appreciated :)

Expected Behavior

I expect the environment variable APP_POOL_ID to be correctly set, even when "Preload = true" (Application Initialization module)

Steps To Reproduce

No response

Exceptions (if any)

No response

.NET Version

.NET 6 or higher

Anything else?

No response