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From "Carlucci, Tony" <>
Subject RE: [users@httpd] Intermittent mod_proxy_ajp error - APR does not understand this error code: proxy: dialog
Date Wed, 25 Jul 2012 12:23:33 GMT
>-----Original Message-----
>From: Rainer Jung []
>Sent: Wednesday, July 25, 2012 5:00 AM
>Subject: Re: [users@httpd] Intermittent mod_proxy_ajp error - APR does not
>understand this error code: proxy: dialog
>On 23.07.2012 20:36, Carlucci, Tony wrote:
>> Hello, I’ve been trying to track down an intermittent problem with a
>> Java web application that is running on tcServer fronted by Apache HTTP
>> Server.    We get intermittent “Server Unavailable / HTTP 500” errors,
>> and when we do see them, there is the same set of log statements written
>> to the Apache HTTP Server error log:
>> [Mon Jul 23 10:03:15 2012] [error] (70014)End of file found:
>> ajp_ilink_receive() can't receive header
>> [Mon Jul 23 10:03:15 2012] [error] ajp_read_header: ajp_ilink_receive failed
>> [Mon Jul 23 10:03:15 2012] [error] (120006)APR does not understand this
>> error code: proxy: dialog to ( failed
>> We are not seeing any error messages in the tcServer logs.
>> I believe the issue is with the mod_proxy_ajp module but it’s been very
>> difficult tracking down what exactly the problem is.   What’s
>> interesting is that this Apache / tcServer configuration is used with
>> other applications that work just fine and never have the intermittent
>> 500 error.   We also can run our application strictly in Tomcat (no
>> Apache front) without any intermittent errors.
>> We haven’t ruled out that there could be something in our Java
>> application code that is causing this, in combination with the
>> mod_proxy_ajp module, but we have hit a wall as to what this issue could
>> be.  Has anyone else experienced a similar intermittent issue combined
>> with the above error messages?  Below is a copy of the error log and
>> some configuration settings.
>You might want to check the following discussion thread:
>To actually narrow down the cause I would:
>- use ping as mentioned in the thread
>- check whether the timeout you have set on the Tomcat connector is
>roughly the same as used by mod_proxy_ajp
>- check whether it looks like happening mostly for the same URL, then it
>is more likely a servlet issue
>- if it happens often enough sniff the traffic between Apache and Tomcat
>and then check the packet details for one of the broken requests. For
>this to work you might need to move Tomcat away from localhost.

Thanks for the suggestions Rainer, I'll give these a try.


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