Check if Asp.Net(Core) application is hosted in IIS

Question

How can I check inside the application if it is being hosted in IIS?

Answer 1

Check if the environment variable APP_POOL_ID is set.

public static bool InsideIIS() =>
    System.Environment.GetEnvironmentVariable("APP_POOL_ID") is string;

All of environment variables that iis sets on a child process

Answer 2

I've tried the answer by Branimir Ričko but found that it's not correct: this environment variable is also set when running under IIS express.

So here is my modified version:

static bool IsRunningInsideIIS() =>
    System.Environment.GetEnvironmentVariable("ASPNETCORE_HOSTINGSTARTUPASSEMBLIES") is string startupAssemblies &&  
 startupAssemblies.Contains(typeof(Microsoft.AspNetCore.Server.IISIntegration.IISDefaults).Namespace);

Answer 3

I believe there is no direct way how to achieve that out of the box. At least I haven't found one. And the reason, as I can tell is the fact ASP.NET Core application is actually a self-contained application knowing nothing about it's parent context, unless the later will reveal information about itself.

For example in the configuration file we can tell which type of the installation we're running: production or development. We can assume that production is IIS, while development is not. However that didn't worked for me. Since my production setup could be either IIS or windows service.

So I have worked around this problem by supplying different command line arguments to my application depending on type of run it supposed to perform. That, actually, came naturally for me, since windows service indeed requires different approach to run.

For example in my case code looked somewhat like so:

namespace AspNetCore.Web.App
{
    using McMaster.Extensions.CommandLineUtils;
    using Microsoft.AspNetCore;
    using Microsoft.AspNetCore.Hosting;
    using Microsoft.AspNetCore.Hosting.WindowsServices;
    using System;
    using System.Diagnostics;
    using System.IO;

    public class Program
    {
        #region Public Methods

        public static IWebHostBuilder GetHostBuilder(string[] args, int port) =>
            WebHost.CreateDefaultBuilder(args)
                .UseKestrel()
                .UseIISIntegration()
                .UseUrls($"http://*:{port}")
                .UseStartup<Startup>();

        public static void Main(string[] args)
        {
            var app = new CommandLineApplication();

            app.HelpOption();
            var optionHosting = app.Option("--hosting <TYPE>", "Type of the hosting used. Valid options: `service` and `console`, `console` is the default one", CommandOptionType.SingleValue);
            var optionPort = app.Option("--port <NUMBER>", "Post will be used, `5000` is the default one", CommandOptionType.SingleValue);

            app.OnExecute(() =>
            {
                //
                var hosting = optionHosting.HasValue()
                    ? optionHosting.Value()
                    : "console";

                var port = optionPort.HasValue()
                    ? new Func<int>(() =>
                    {
                        if (int.TryParse(optionPort.Value(), out var number))
                        {
                            // Returning successfully parsed number
                            return number;
                        }

                        // Returning default port number in case of failure
                        return 5000;
                    })()
                    : 5000;

                var builder = GetHostBuilder(args, port);

                if (Debugger.IsAttached || hosting.ToLowerInvariant() != "service")
                {
                    builder
                        .UseContentRoot(Directory.GetCurrentDirectory())
                        .Build()
                        .Run();
                }
                else
                {
                    builder
                        .UseContentRoot(Path.GetDirectoryName(Process.GetCurrentProcess().MainModule.FileName))
                        .Build()
                        .RunAsService();
                }
            });

            app.Execute(args);
        }

        #endregion Public Methods
    }
}

This code not only allows select type of the hosting (service and console — the option that IIS supposed to use), but also allows to change port which is important, when you're running as Windows service.

Another good thing is usage of argument parsing library, McMaster.Extensions.CommandLineUtils — it will show information about configured command line switches, so it would be easy to select right values.