1. Phil0001

    We were getting 503 errors from a single server out of 30. One thing that threw us initially is that the 503 errors no longer appear to be logged into the IIS request log on 2012R2 (as they we with IIS7/7.5). After searching these IIS request logs for ages and finding nothing we eventually found 503 in FREB and http.sys log. Any idea where this change is documented, is it your understanding that these 503 should \ should not now be in the IIS request log? Any idea why this change?

  2. Hi Phil,

    The 503s are usually not logged in the IIS log/FREB, because they represent errors that occur before the request is received by the IIS worker process. They will typically end up in the HTTPERR log and if they are due to a application pool failure, there may also be some eventlog events in the Application log.

    There are a couple exceptions, particularly 503s due to ASP.NET and IIS concurrency limits. Those will show up in the IIS logs because they are worker-process level failures.

    FWIW, LeanSentry automatically tracks these, as well as other causes of application pool failure, so give it a try if you are having trouble.

    Hope this helps!


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