Could not load file or assembly 'Microsoft.AspNet.SessionState.SessionStateModule' when accessing .Net core api via "/api" virtual path

Question

Could not load file or assembly 'Microsoft.AspNet.SessionState.SessionStateModule' when accessing .Net core api via "/api" virtual path

Georgi Koemdzhiev 61

I deployed the following apps:

ASP.NET MVC (.Net Framework 4.7.2) site
.Net Core 3.1 web API

both on the same IIS server. The site is set up to "/" path and the API to "/api":

Accessing the website from, for example, from localhost opens site fine. However, if I try to access the API (e.g. http://localhost/api) I get this error:

Could not load file or assembly 'Microsoft.AspNet.SessionState.SessionStateModule, Version=1.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.   
  Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.   
  
 Exception Details: System.IO.FileNotFoundException: Could not load file or assembly 'Microsoft.AspNet.SessionState.SessionStateModule, Version=1.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.  
  
Source Error:   
  
 An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.     
  
Assembly Load Trace: The following information can be helpful to determine why the assembly 'Microsoft.AspNet.SessionState.SessionStateModule, Version=1.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' could not be loaded.  
  
Assembly manager loaded from:  C:\Windows\Microsoft.NET\Framework64\v4.0.30319\clr.dll  
Running under executable  c:\windows\system32\inetsrv\w3wp.exe  
--- A detailed error log follows.   
  
=== Pre-bind state information ===  
LOG: DisplayName = Microsoft.AspNet.SessionState.SessionStateModule, Version=1.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35  
 (Fully-specified)  
LOG: Appbase = file:///C:/inetpub/AspNetCoreWebApps/BackendAPI/  
LOG: Initial PrivatePath = C:\inetpub\AspNetCoreWebApps\BackendAPI\bin  
Calling assembly : (Unknown).  
===  
LOG: This bind starts in default load context.  
LOG: Using application configuration file: C:\inetpub\AspNetCoreWebApps\BackendAPI\web.config  
LOG: Using host configuration file: C:\Windows\Microsoft.NET\Framework64\v4.0.30319\aspnet.config  
LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework64\v4.0.30319\config\machine.config.  
LOG: Post-policy reference: Microsoft.AspNet.SessionState.SessionStateModule, Version=1.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35  
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework64/v4.0.30319/Temporary ASP.NET Files/api/27eecc96/2976b187/Microsoft.AspNet.SessionState.SessionStateModule.DLL.  
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework64/v4.0.30319/Temporary ASP.NET Files/api/27eecc96/2976b187/Microsoft.AspNet.SessionState.SessionStateModule/Microsoft.AspNet.SessionState.SessionStateModule.DLL.  
LOG: Attempting download of new URL file:///C:/inetpub/AspNetCoreWebApps/BackendAPI/bin/Microsoft.AspNet.SessionState.SessionStateModule.DLL.  
LOG: Attempting download of new URL file:///C:/inetpub/AspNetCoreWebApps/BackendAPI/bin/Microsoft.AspNet.SessionState.SessionStateModule/Microsoft.AspNet.SessionState.SessionStateModule.DLL.  
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework64/v4.0.30319/Temporary ASP.NET Files/api/27eecc96/2976b187/Microsoft.AspNet.SessionState.SessionStateModule.EXE.  
LOG: Attempting download of new URL file:///C:/Windows/Microsoft.NET/Framework64/v4.0.30319/Temporary ASP.NET Files/api/27eecc96/2976b187/Microsoft.AspNet.SessionState.SessionStateModule/Microsoft.AspNet.SessionState.SessionStateModule.EXE.  
LOG: Attempting download of new URL file:///C:/inetpub/AspNetCoreWebApps/BackendAPI/bin/Microsoft.AspNet.SessionState.SessionStateModule.EXE.  
LOG: Attempting download of new URL file:///C:/inetpub/AspNetCoreWebApps/BackendAPI/bin/Microsoft.AspNet.SessionState.SessionStateModule/Microsoft.AspNet.SessionState.SessionStateModule.EXE.  
  
Stack Trace:   
  
[FileNotFoundException: Could not load file or assembly 'Microsoft.AspNet.SessionState.SessionStateModule, Version=1.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.]  
   System.RuntimeTypeHandle.GetTypeByName(String name, Boolean throwOnError, Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMarkHandle stackMark, IntPtr pPrivHostBinder, Boolean loadTypeFromPartialName, ObjectHandleOnStack type) +0  
   System.RuntimeTypeHandle.GetTypeByName(String name, Boolean throwOnError, Boolean ignoreCase, Boolean reflectionOnly, StackCrawlMark& stackMark, IntPtr pPrivHostBinder, Boolean loadTypeFromPartialName) +96  
   System.Type.GetType(String typeName, Boolean throwOnError, Boolean ignoreCase) +65  
   System.Web.Compilation.BuildManager.GetType(String typeName, Boolean throwOnError, Boolean ignoreCase) +62  
   System.Web.Configuration.ConfigUtil.GetType(String typeName, String propertyName, ConfigurationElement configElement, XmlNode node, Boolean checkAptcaBit, Boolean ignoreCase) +50  
  
[ConfigurationErrorsException: Could not load file or assembly 'Microsoft.AspNet.SessionState.SessionStateModule, Version=1.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.]  
   System.Web.Configuration.ConfigUtil.GetType(String typeName, String propertyName, ConfigurationElement configElement, XmlNode node, Boolean checkAptcaBit, Boolean ignoreCase) +572  
   System.Web.Configuration.ConfigUtil.GetType(String typeName, String propertyName, ConfigurationElement configElement, Boolean checkAptcaBit) +31  
   System.Web.Configuration.Common.ModulesEntry.SecureGetType(String typeName, String propertyName, ConfigurationElement configElement) +59  
   System.Web.Configuration.Common.ModulesEntry..ctor(String name, String typeName, String propertyName, ConfigurationElement configElement) +59  
   System.Web.HttpApplication.BuildIntegratedModuleCollection(List`1 moduleList) +221  
   System.Web.HttpApplication.GetModuleCollection(IntPtr appContext) +1103  
   System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers) +122  
   System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context) +173  
   System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context) +255  
   System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext) +347  
  
[HttpException (0x80004005): Could not load file or assembly 'Microsoft.AspNet.SessionState.SessionStateModule, Version=1.1.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.]  
   System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +552  
   System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +122  
   System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +737

dotnet --info output on the server:

PS C:\Users\Administrator> dotnet --info  
.NET SDK (reflecting any global.json):  
 Version:   5.0.401  
 Commit:    4bef5f3dbf  
  
Runtime Environment:  
 OS Name:     Windows  
 OS Version:  10.0.14393  
 OS Platform: Windows  
 RID:         win10-x64  
 Base Path:   C:\Program Files\dotnet\sdk\5.0.401\  
  
Host (useful for support):  
  Version: 5.0.10  
  Commit:  e1825b4928  
  
.NET SDKs installed:  
  2.1.818 [C:\Program Files\dotnet\sdk]  
  3.1.413 [C:\Program Files\dotnet\sdk]  
  5.0.401 [C:\Program Files\dotnet\sdk]  
  
.NET runtimes installed:  
  Microsoft.AspNetCore.All 2.1.30 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]  
  Microsoft.AspNetCore.App 2.1.30 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]  
  Microsoft.AspNetCore.App 3.1.19 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]  
  Microsoft.AspNetCore.App 5.0.10 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]  
  Microsoft.NETCore.App 2.1.30 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]  
  Microsoft.NETCore.App 3.1.19 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]  
  Microsoft.NETCore.App 5.0.10 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]  
  Microsoft.WindowsDesktop.App 3.1.19 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]  
  Microsoft.WindowsDesktop.App 5.0.10 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

The strange thing is that the API project (.Net Core 3.1) does not use "Microsoft.AspNet.SessionState.SessionStateModule" package at all. However, this SessionStateModule package is used by the .Net Framework site (via a classic/4.7.2 library).

I do not understand why the assembly binder (i.e. Fusion) is looking for that package in the "C:\inetpub*BackendAPI\bin folder. There is no "bin" folder where the .Net Core 3.1 app is deployed at all (see LOG: Initial PrivatePath = C:\inetpub\AspNetCoreWebApps\BackendAPI\bin).

What am I missing here? Have a messed up the deployment of those 2 apps somehow?

Thank you in advance

Accepted answer

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Answer 1

Michael Taylor 60,161

That isn't going to work. Your main app is hosted by .NET Framework. That is what the app pool is running. You are then trying to host a child app using .NET Core. You can have 2 child apps running different versions of the runtime but the scenario you are trying isn't supported AFAIK.

Separate your main site from the api and host them in 2 different apps under the default web site. You can using bindings on the default site if you need to make them accessible using specific DNS names. Alternatively move the API to its own site altogether and use bindings to manage traffic to each site.

Georgi Koemdzhiev 61 Reputation points

2021-11-01T08:55:18.09+00:00

Thank you! Could you please explain what you mean by this

You can have 2 child apps running different versions of the runtime

Do you mean that I can have a child app of my .Net Framework 4.7.2 app and it can run say 4.6.2?
Michael Taylor 60,161 Reputation points

2021-11-01T14:03:03.14+00:00

.NET 4.7.2 and .NET 4.6.2 are the same runtime so it doesn't matter. All 4.x apps share the same runtime.

My recommendation is to create either a separate web site (if you're using DNS) or a different app under the default web site to host your main app (e.g. myapp). For this app have the app run running the managed code - integrated. You can either create a new one (if you need to run under a custom account) or use the existing .NET v4.5 app pool that is already defined.

Your API (which is already a child app) should be running under a different app pool that doesn't have any managed code in it. You will need to probably create this app pool but make sure no CLR is selected.

Now you have 2 different apps running under the same site. Each app is using its own app pool. This will prevent you from running into odd problems given how you originally had it and should resolve your issue. The downside is that your URLs will now look something like https://myserver/myapp/default.html instead of https://myserver/default.html. If that is a concern for you then create DNS entries and add bindings to your sites to hide the details.
Georgi Koemdzhiev 61 Reputation points

2021-11-01T15:07:42.763+00:00

Thank you for the detailed explanation.

Just to make sure that I understand correctly. If I would like to have subdomains for my sites (https://api.myserver.com & https://mysite.myserver.com), I must use separate IIS Applications. Am I correct?
Michael Taylor 60,161 Reputation points

2021-11-01T15:35:35.263+00:00

You can have any # of DNS names pointing to the same site so technically you don't need separate apps but in your specific case you would have 2 different apps. However you should understand how bindings work because you're potentially going to run into unexpected behavior. Imagine you associate mysite.myserver.com to your default website. To get to your api the url would be mysite.myserver.com/api. Subapps are always based upon the DNS of the website. You decide you want to "hide" the fact that this is an app so you add the api.mserver.com binding to the default site as well. Now the API url is api.myserver.com/api. But the following urls would also be valid: mysite.myserver.com/api, 'myapi.myserver.com/app`, etc.

The purpose of DNS in IIS is to map a friendly name to a website. Normally if you go to a website (such as myserver.com) then the default website is loaded. If you have multiple websites then you cannot get to the other one's directly. To work around this you can assign a site a non-default port (e.g. 8081) but now anyone using the site has to remember to use the port as well (e.g. myserver.com goes to default site, myserver.com:8081 goes to second site). To avoid this craziness we use DNS. Each site can specify the DNS names it listens for. When a request comes to the server the DNS name determines the site to call.
Michael Taylor 60,161 Reputation points

2021-11-01T15:41:43.26+00:00

In order to host your apps using the DNS names you want (and not allowing the others) then you actually need 2 web sites. One can be the default website if you want so we'll assume your default web site is your main site. Add a site binding to the default website that associates mysite.myserver.com to it. Be sure to do both HTTP and HTTPS.
Create a new web site on the same server (the api site). Move your API to that site (get rid of the child api folder, you don't need it). The api site will use the app pool that is not configured to use managed code while the default web site will continue to use the app pool with managed code.

Now bind the api.myserver.com DNS name to your api site. You are now hosting 2 web sites (main site and api site). One uses NF and one use NC. Each respond to different DNS names.

Note that the actual name of the website in IIS is irrelevant if you're using DNS bindings but I find it useful to match them up to make it easier to remember.
Georgi Koemdzhiev 61 Reputation points

2021-11-01T15:46:13.043+00:00

Thank you very much for your time. I do understand what I need to do now with regards to the DNS names and bindings. I tried publishing the 2 apps I have as suggested by you (and also Bruce) - using separate IIS Apps and No Managed Code and I no longer get the "Could not load file or assembly" exception.
Georgi Koemdzhiev 61 Reputation points

2021-11-01T16:11:00.587+00:00

Thank you again! I find the information you have shared with me very valuable, it is my first time dealing with IIS server setup and I have learned a lot here :)

Answer 2

Bruce (SqlWork.com) 77,686 Volunteer Moderator

I tried your config. asp.net 4.8 application with an api folder (app) hosting a core 3.1 webapi application

it looks like you did not create the api application correctly

it should be a new Application with its own unique app pool set to no managed code
the physical path should be a folder that the core 3.1 app published to. (should not be a subfolder of the parent site). looking at your logs it should probably be:

c:\inetpub\AspNetCoreWebApps\BackendAPI

there should just be a web.config, and the app.exe and depend dll's in the folder. the web.config should look like:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <location path="." inheritInChildApplications="false">
    <system.webServer>
      <handlers>
        <add name="aspNetCore" path="*" verb="*" modules="AspNetCoreModuleV2" resourceType="Unspecified" />
      </handlers>
      <aspNetCore processPath="dotnet" arguments=".\backendapi.dll" stdoutLogEnabled="false" stdoutLogFile=".\logs\stdout" hostingModel="inprocess" />
    </system.webServer>
  </location>
</configuration>

Georgi Koemdzhiev 61 Reputation points

2021-11-01T09:00:06.557+00:00

Thank you Bruce!

I checked the web.config for my .Net Core app and it is exactly the same as the one you have above. As @Michael Taylor also mentioned, the problem I am experiencing must be to do with the fact that the .Net Core app is running on .Net Framework runtime (i.e. the pool is using managed code). I will try to separate the 2 apps so that they are both siblings under the Default site and not nested having the core app set to No Managed core. Will see if that will fix the issue
Bruce (SqlWork.com) 77,686 Reputation points Volunteer Moderator

2021-11-02T14:37:07.25+00:00

I had no trouble nesting. Be sure the core app has it own unmanaged app pool.

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Could not load file or assembly 'Microsoft.AspNet.SessionState.SessionStateModule' when accessing .Net core api via "/api" virtual path

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