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I am working on a large web application with a C# backend. In the development setup, the application is served via an IIS 8.5 instance on my machine.

Since recently, I cannot log in any more. I still get the log in form, but once I click Log in after entering my user data, Chrome's network view shows the request is answered with an error 503 / Service unavailable response from the server.

I have enabled Failed Request Tracing for all status codes between 200 and 999 for the entire site in IIS Manager, and I have enabled failed request tracing in the configuration settings in IIS Manager's sitebar.

All requests related to retrieving the log in form are duly logged to C:\inetpub\logs\FailedReqLogFiles\W3SVC1, but not a single request log file appears when clicking the Log in button.

As per company policy, I do not have any access to the sources of the code that handles the log in request, and everyone that does is currently, and for the two weeks to come, in their summer vacation - but as there is no request log, I somehow suspect that particular request never gets far enough to even touch our web application.

How can I find out what is happening to cause the 503 response?

O. R. Mapper
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  • You can try checking [other logs related to IIS](https://peter.hahndorf.eu/blog/iislogging.html) – Peter Hahndorf Aug 16 '16 at 18:10
  • @PeterHahndorf: Oh, excellent. I had checked some of these (such as Windows event log), but in my case, `HTTPERR` provided me with the decisive hint. – O. R. Mapper Aug 17 '16 at 06:38

1 Answers1

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In addition to the normal IIS logs and Failed Request tracing, there are other logs that you may want to check for problems.

  • The Windows Event Log
  • The httperr log
  • ASP.NET health monitoring logs
  • http.sys trace logs

I wrote a blog post which describes these in more detail.

Peter Hahndorf
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  • The `httperr` log led me to recognize that one of my app pools had stopped working as the authentication data was not valid any more. I have no idea why it (1) changed or (2) had become invalid because I (1) had not touched the app pool configuration for quite a while and (2) my last password reset was more than a month ago. – O. R. Mapper Aug 17 '16 at 09:49