title: Mysterious IIS Problem: Site stops serving dynamic pages, no errors in logs
body: <p>This may be the most mysterious problem I've ever encountered.</p>
  
  <p>We have an IIS7 install with 3 Web Sites on it, each with it's own Application Pool.  Once a day, for about an hour, a specific one of them goes down.</p>
  
  <p>What I mean by "goes down" is:</p>
  
  <ol>
  <li>It stops responding to requests for dynamic pages (ex. default.aspx) but will serve static files fine (logo.png).</li>
  <li>Wireshark tells me that these dynamic page requests are actually return HTTP 500 Internal Server errors, but in the browser, I don't see an error.  I just see the browser spinning.</li>
  <li>If I log on <strong>locally to the box</strong> and surf around <strong>everything runs fine</strong>.  All the pages pull up, so the database is being queried.  It all seems perfectly normal.</li>
  <li>There are no errors in the event log.</li>
  <li>There are no errors recorded that have been captured by our internal (Application-level) error logging.</li>
  <li>The basic IIS log file, which I thought logged every request, shows <strong>no record</strong> of these requests coming in.</li>
  </ol>
  
  <p>And, if I restart the App Pool for the Web Site, everything comes back immediately.  Or, if I just wait an hour or so, it comes back.</p>
  
  <p>So, I've ruled out:</p>
  
  <ol>
  <li>DNS issues, since I have no problem terminal servicing into the box by hostname.</li>
  <li>Database issues, since the site works fine when I'm local to the box and surfing around</li>
  <li>HTTP firewall issues, since I'm seeing the requests in wireshark, and am even getting images to serve up.</li>
  </ol>
  
  <p>I have to assume it's a problem with my application, but IIS doesn't even show that these requests ever happened, and nothing in IIS or my app is logging errors.</p>
  
  <p>It also doesn't even go down at the same time each day.  This started at night (@midnight) and seems that it's gradually started moving it's daily time by an hour or so, until the point now where it hit at 9AM.</p>
  
  <p>Any clues you might have for further troubleshooting would be greatly appreciated.</p>
  
  <p>Tom </p>