HTTP Error 503. The service is unavailable. App pool stops on accessing website

Question

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 b

Answer 1

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

Answer 2

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.

Answer 3

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.

Answer 4

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.

Answer 5

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

Answer 6

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.