[c#] HTTP Error 503. The service is unavailable. App pool stops on accessing website

There are number of posts on this and I have tried many a things by now. But to no avail. Myself a Winforms Developer basically, started working on this Web stuff few days back as my company is taking Web initiatives.

I have a ASP.Net project and I want to host it on local IIS. In Project properties -> Web settings I chose Use Local IIS Server and gave a url as localhost/MyApp. I tried accessing it on my firefox browser and received error as HTTP Error 503. The service is unavailable.

Previously I got many other errors and I one by one fixed them all. But struck with this one. These are the settings I have in my project

1. Application Pool set to ASP.Net v4.0 Classic
2. App Pool Enable 32 bit Application property is true
3. App Pool is started
4. Project build property set to Any CPU for Target framework

But I would like to mention a weird behavior. Following is something that I am facing

1. Application Pool is Started
2. I try to access my local website (by giving url as localhost/MyApp)
3. I receive the error as HTTP Error 503. The service is unavailable
4. Application Pool is Stopped

I have seen following link and I have already tried it. For the above behavior I reached here. According to this link, Computer name should not have . in it. I don't have any . in my Computer name but do have - in it. Also my domain name contains . in it. Moreover I can't change these settings as its my office laptop and our TFS settings are bound to our Domain and Computer Names.

Can anyone help me to understand whats happening? Please guide me. Thanks.

Edit

I have following code in Global.asax. Application_BeginRequest method is empty in same file.

protected override void Application_Start(object sender, EventArgs e)
{
    base.Application_Start(sender, e);
    String _path = String.Concat(System.AppDomain.CurrentDomain.RelativeSearchPath, ";",
                                         System.Environment.GetEnvironmentVariable("PATH"));
    System.Environment.SetEnvironmentVariable("PATH", _path, EnvironmentVariableTarget.Process);
    MyAppLog.Initialize();
    MyAppLog.WriteMessage("Application Started");
}

Update

As per the suggestions in Comment, I am able to run the website from Cassini.

In addition to the steps outlined at this link from Orhan's answer, you may need to additionally remove the native module by going to IIS Manager > Server Root > Modules > Configure Native Modules. Select MfeEngine and then select Remove.

I had a similar issue. I solved it by adding my user to the "Log on as a batch job" policy under "Local Security Policy" > "Local Policies" > "User Rights Assignment".

Changing "Managed Pipeline Mode" from "Classic" to "Integrated" worked for me. It can be changed at Application Pools -> Basic Settings

For my situation is that my login password changed, while the application pool still uses the old one. So just click the "Advanced Settings" of your application pool and reset your "Identity".

Just to add to these Anniversary Update issues (thanks Microsoft) if the file you are missing is cgi.dll, ie your Event Viewer has

The Module DLL C:\WINDOWS\System32\inetsrv\cgi.dll failed to load.  The data is the error.

Then to fix this:

1. Go to IIS Manager
2. Select the very top row in the Connections panel (typically your PC name)
3. At the very bottom of the right panel, under Management, you should have Web Platform Installer
4. Once that loads, select Products
5. In the search type in cgi then hit <Enter>
6. Select IIS: CGI then click Add on the right and finally Install on the bottom
7. After installing it should force you to restart your PC and you should be fixed.

In my case I checked event logs and found error was Cannot read configuration file ' trying to read configuration data from file '\\?\', line number '0'. The data field contains the error code.

The error code was 2307.

I deleted all files in C:\inetpub\temp\appPools and restarted the iis. It fixed the issue.

When I first time add the service and created the app pool for it. I did "iisreset" from command prompt, and it worked.

Most of Time, it was occured due to AppPool Setting.

Check the following to resolve this

1. Check Apppool service is running.
2. Check Identity of AppPool.
3. Enter the new password if it has changed for that identity.

The following Images show these setting in IIS

For anyone coming here with Windows 10 and after updating them to Anniversary update, please check this link, it helped me:

https://orcharddojo.net/blog/troubleshooting-iis-apppool-crashes-status-503-after-windows-10-anniversary-update

In case link goes down: If your Event log shows that aspnetcore.dll, rewrite.dll (most often, but could be others as well) failed to load, you have to repair the missing items.

Here are two specific issues we've experienced so far and how to fix them, but you may bump into completely different ones:

"C:\WINDOWS\system32\inetsrv\rewrite.dll" (reference)
    Go to "Programs and Features" (Win+X, F) and repair "IIS URL Rewrite Module 2".
"C:\WINDOWS\system32\inetsrv\aspnetcore.dll" (reference)
    Go to "Programs and Features" (Win+X, F) and repair "Microsoft .NET Core 1.0.0 - VS 2015 Tooling ...".

Ok, I have another solution for one specific case: if you use WINDOWS 10, and you updated it recently (with Anniversary Update package) you need to follow the steps below:

1. Check your Windows Event Viewer - press Win+R and type: eventvwr, then press ENTER.
2. On the left side of Windows Event Viewer click on Windows Logs -> Application.
3. Now you need to find some ERRORS for source IIS-W3SVC-WP in middle window.
4. Probably you will see message like:

The Module DLL >>path-to-DLL<< failed to load. The data is the error.

5. You have to go to Control Panel -> Program and Features and depending on which dll cannot be load you need to repair another module:
   • for rewrite.dll - find IIS URL Rewrite Module 2 and click Change->Repair
   • for aspnetcore.dll - find Microsoft .NET Core 1.0.0 - VS 2015 Tooling ... and click Change->Repair.
6. Restart your computer.

I had the same issue with iis 8.5. After searching the eventViewer under windows Logs-->applications, I realized that I'm having a permission error for the machine.config file of the .net framework located at "C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config\machine.config". Giving it a permission for IIS_IUSRS solved my problem (right click the file-->properties-->security-->edit-->add-->IIS_IUSRS)

Will this answer Help you?
If you are receiving the following message in the EventViewer

The Module DLL aspnetcorev2.dll failed to load. The data is the error.

Then yes this will solve your problem

To check your event Viewer

1. press Win+R and type: eventvwr, then press ENTER.
2. On the left side of Windows Event Viewer click on Windows Logs -> Application.
3. Now you need to find some ERRORS for source IIS-W3SVC-WP in the middle window.

Install Microsoft Visual C++ 2015 Redistributable 86x AND 64X (both of them)

Source

If you can run the website in Visual Studio debugger, then might be able to see where in your code the application pool is crashing. In my case, it was a function being called recursively an unlimited number of times, and that caused a stack overflow. Note: the Windows event log and the IIS logs were not helpful to diagnose the problem.

One possible reason this might happen is that you don't have enough disk space in your server machine. You can find more information in event viewer. if such thing happen, just stop the IIS, clean some free disk space and restart the IIS and then start the App Poll.

If you have McAfee HIPS and if you see the following error in event viewer application log:

The Module DLL C:\Windows\System32\inetsrv\HipIISEngineStub.dll failed to load.
The data is the error.

Then the following resolved the issue in my case: https://kc.mcafee.com/corporate/index?page=content&id=KB72677&actp=LIST

Quote from the page:

1. Click Start, Run, type explorer and click OK.
2. Navigate to: %windir%\system32\inetsrv\config
3. Open the file applicationHost.config as Administrator for editing in Notepad.

4. Edit the <globalModules> section and remove the following line:
   <add name="MfeEngine" image="%windir%\System32\inetsrv\HipIISEngineStub.dll" />

5. Edit the <modules> section and remove the following line:
   <add name="MfeEngine" />

6. After you have finished editing the applicationHost.config file, save the file, then restart the IIS server using iisreset or by restarting the system.

In my case error message displaed in Windows Event Viewer -> Windows Logs -> Application was "The Module DLL C:\Windows\system32\inetsrv\rewrite.dll failed to load. The data is the error." Uninstalling rewrite module via installer solved the problem. I wasn't using any rewrite rules so I uninstalled rewrite module. Reinstalling the module may help the problem as well.

I was facing the same problem, and debugged it using the event logs. First it said that : "The description for Event ID 5059 from source Microsoft-Windows-WAS cannot be found".

I then turned on WAS using turn windows features on/off. Then i saw this in eventvwr "Microsoft-Windows-DistributedCOM cannot be found".

Finally I gave up and deleted the App Pool (that used to stop on accessing the website) and created it again, as it is. This resolved the problem.

I had a similar issue, all my app pools were stopping whenever a web request was made to them. Although I was getting the following error in the Event Viewer:

The worker process for application pool 'appPoolName' encountered an error 'Configuration file is not well-formed XML ' trying to read configuration data from file '\?\C:\inetpub\temp\apppools\appPoolName\appPoolName.config', line number '3'. The data field contains the error code.

Which told me that there were errors in the application.config at:

C:\Windows\System32\inetsrv\config\applicationHost.config

In my scenario, I edited the web.config on deploy with an element IIS clearly dislikes, the applicationHost.config scraped the web.config and inserted this bad element and wouldn't resolve until I manually removed it

I was experiencing this error and in my case the cause was that some time ago I modified the user password, and the 503 error didn't appears till I restarted the application pool.

So I fixed it setting the new password on Applications Pools / Advanced Settings / Identity / [...] / Set... / Password / Confirm Password