IIS ASP.NET 6 startup throws System.IO.DirectoryNotFoundException: D:\agent\_work\38\s\IdentityServer\wwwroot\

Question

We are updating one of our applications, in this case IdentityServer, from .NET 5 to .NET 6. It is being hosted by IIS and deployed by Azure Devops Services. The issue we are seeing is that on our development environment the website fails to load but on our staging environment it runs just fine. The error we are seeing on development is

12:45:37.519|Fatal|1||Host terminated unexpectedly.||
System.IO.DirectoryNotFoundException: D:\agent\_work\38\s\IdentityServer\wwwroot\
   at Microsoft.Extensions.FileProviders.PhysicalFileProvider..ctor(String root, ExclusionFilters filters)
   at Microsoft.Extensions.FileProviders.PhysicalFileProvider..ctor(String root)
   at Microsoft.AspNetCore.Hosting.StaticWebAssets.StaticWebAssetsLoader.<>c.<UseStaticWebAssetsCore>b__1_0(String contentRoot)
   at Microsoft.AspNetCore.StaticWebAssets.ManifestStaticWebAssetFileProvider..ctor(StaticWebAssetManifest manifest, Func`2 fileProviderFactory)
   at Microsoft.AspNetCore.Hosting.StaticWebAssets.StaticWebAssetsLoader.UseStaticWebAssetsCore(IWebHostEnvironment environment, Stream manifest)
   at Microsoft.AspNetCore.Hosting.StaticWebAssets.StaticWebAssetsLoader.UseStaticWebAssets(IWebHostEnvironment environment, IConfiguration configuration)
   at Microsoft.AspNetCore.WebHost.<>c.<ConfigureWebDefaults>b__9_0(WebHostBuilderContext ctx, IConfigurationBuilder cb)
   at Microsoft.AspNetCore.Hosting.GenericWebHostBuilder.<>c__DisplayClass9_0.<ConfigureAppConfiguration>b__0(HostBuilderContext context, IConfigurationBuilder builder)
   at Microsoft.Extensions.Hosting.HostBuilder.BuildAppConfiguration()
   at Microsoft.Extensions.Hosting.HostBuilder.Build()
   at IdentityServer.Program.Main(String[] args) in D:\agent\_work\38\s\IdentityServer\Program.cs:line 23

The path it reports, D:\agent\_work\38\s\IdentityServer\wwwroot\ is interesting because that path is the same as the path from the DevOps build machine. We don't see this error if we revert back to .NET 5 and we don't see the problem on our staging machine.

The Program.cs class is defined as

using System;
using Microsoft.AspNetCore;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;
using NewRelic.LogEnrichers.Serilog;
using Serilog;
using Serilog.Events;

namespace IdentityServer
{
    public class Program
    {
        public static int Main(string[] args)
        {
            try
            {
                CreateLogger();
                Log.Information("Starting host...");
                CreateHostBuilder(args).Build().Run();
                return 0;
            }
            catch (Exception ex)
            {
                Log.Fatal(ex, "Host terminated unexpectedly.");
                return 1;
            }
            finally
            {
                Log.CloseAndFlush();
            }
        }

        public static void CreateLogger()
        {
            var configuration = GetConfiguration();
            Log.Logger = new LoggerConfiguration()
                .ReadFrom.Configuration(configuration)
                .Enrich.FromLogContext() // allows logging middleware to inject output values
                .Enrich.WithThreadId()
                .Enrich.WithNewRelicLogsInContext()
                .CreateLogger();
        }

        public static IHostBuilder CreateHostBuilder(string[] args)
        {
            var configuration = GetConfiguration();
            return Host.CreateDefaultBuilder(args)
                .ConfigureWebHostDefaults(
                    webBuilder =>
                    {
                        webBuilder.UseConfiguration(configuration);
                        webBuilder.UseSerilog();
                        webBuilder.UseIIS();
                        webBuilder.CaptureStartupErrors(true);
                        webBuilder.UseStartup<Startup>();
                    });
        }

        private static IConfiguration GetConfiguration()
        {
            var environment = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT");
            var builder = new ConfigurationBuilder()
                .AddJsonFile("appsettings.json")
                .AddJsonFile($"appsettings.{environment}.json", true, true);
            var configuration = builder.Build();

            return configuration;
        }
    }
}

We do have other .NET 6 web applications running just fine on this instance of IIS. I was thinking that the problem might be in our release pipelines but they are identical in their task configurations between the environments. Tried looking for the directory path in the code or configuration but don't see it anywhere. Have tried manually setting the WebRoot and ContentRoot paths via .UseWebRoot("path to folder") and .UseContentRoot("path to folder") in the Program.cs but didn't see any change in the logs or the app starting.

Even updated the web.config file to have the exact path for executing the project dll in the aspNetCore element but still no change.

Update 10 Feb 2022

Added debug output to the startup to verify file and folder paths. Everything in the environment variables and execution file path look correct.

ASPNETCORE_IIS_PHYSICAL_PATH - C:\inetpub\webapps\IdentityServer\
Executable Path: C:\inetpub\webapps\IdentityServer\IdentityServer.dll

Answer 1

The problem ended up being how we were pushing our updates out to the servers from DevOps. Our pipelines were built to copy over files out of the Release directory of the build folder. One of the problems with this approach is that files not needed for a site to run but generated during a build are also copied to the release server. In this case, a new file which is generated in .NET 6, .staticwebassets.runtime.json, was getting copied to our servers.

The way .NET 6 seems to behave is that if the environment is set to Development then it will look for this file to figure out where the static web assets are located. If the file doesn't exist then it will assume the files are in a wwwroot sub-directory of the site. This makes sense for instances where you are running the project from your local Visual Studio. More details about this file are available in another SO post with links to the source code in GitHub. To fix our problem we changed our release pipeline to use the publish.zip file that is generated when you run the publish command on a solution. The archive only contains the files needed to run the site, so none of the extraneous files like .staticwebassets.runtime.json are included. We should have been doing this the whole time... lesson learned.

We now unzip the publish.zip file, apply any file transformations, then copy the unzipped files to the web server.

Answer 2

I initially created an ASP.NET Core Web App but meant to go with an API. I deleted the wwwroot folder and pages folder. I attempted to run debugger and ran into this exception.

System.IO.DirectoryNotFoundException: "\wwwroot\"

I received the error at this line (default template logic)

var builder = WebApplication.CreateBuilder(args)

After investigating, I found that there was no reference to the wwwroot folder in my project file (*.csproj), which was puzzling since I thought this might be the source of the problem.

Solution:

• Add the wwwroot Folder Back: I added the wwwroot folder back to my project, which resolved the issue.

• Clean Build: Alternatively, I found that removing the wwwroot folder and performing a "clean build" (by right-clicking on the solution in Solution Explorer and selecting "Clean Solution") also resolved the issue.

Additional Notes:

Understanding the Issue: The wwwroot folder is typically used to serve static files in an ASP.NET Core application. If a part of your middleware or configuration still expects this folder to exist, it might cause the exception. Even if you switch to a Web API project, some default configurations or dependencies might still look for this directory.

Tips for Others Facing Similar Issues: Make sure to review the middleware configuration and project settings if you face a similar problem. Look for any references to static files or the wwwroot directory. Also, remember that cleaning the build (by rebuilding the solution) might help remove lingering references to deleted files or directories.