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From Rainer Jung <rainer.j...@kippdata.de>
Subject Re: ajp_read_header: ajp_ilink_receive failed
Date Mon, 06 Apr 2009 23:16:18 GMT
On 07.04.2009 01:01, John Oliver wrote:
> On Tue, Apr 07, 2009 at 12:40:42AM +0200, Rainer Jung wrote:
>>> [Sun Mar 29 04:05:33 2009] [error] ajp_read_header: ajp_ilink_receive
>>> failed
>>> [Sun Mar 29 04:05:33 2009] [error] (120006)APR does not understand this
>>> error code: proxy: read response failed from (null) (localhost)
>>
>> 120006 should be AJP_ENO_HEADER, which means after sending a request to
>> the backend, Apache was not able to receive the headers of the response.
>>
>> This could have multiple reasons, like a timeout while waiting for the
>> response, and maybe also a backend closing a connection due to an idle
>> timeout. You should configure Cping/Cpong on mod_proxy_ajp (with a
>> recent version) to allow for robust detection of a broken backend.
> 
> OK...
> 
> What is the "CPING / CPONG For Dummies" version? :-)
> 
> I found
> http://tomcat.apache.org/connectors-doc/generic_howto/timeouts.html
> which doesn't really help me... it presupposes that I know an awful lot
> more than I do.
> 
> Is there a walkthrough somewhere that tells me how I'd go about CPINGing
> and CPONGing that starts with the assumption that I have no idea what
> they are? :-)

The docs for the configuration of all mod_proxy sub modules (like
mod_proxy_ajp) are combined in

http://httpd.apache.org/docs/2.2/mod/mod_proxy.html

Look for "CPING" in the page and then have a look at all those
configuration attributes contained in the surrounding table. Many of
those are well explained. If not, aks here again or on the httpd list.
The CPING for mod_proxy_ajp and for mod_jk (that's the docs page you
found) work the same way. CPING sends an AJP packet to the backend, that
has an empty body (contains no http request). Such a packet is
immediately answered by the connector of the backend with minimal
processing and ensures, that the connection is still working and there
is something speaking AJP13 on the other side. Overhead is very small,
so it's fine to use it before every request.

Regards,

Rainer

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