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From Damian Traverso <>
Subject [users@httpd] mod_proxy_ajp (2.2.13) + Tomcat 6.0.20 - APR does not understand this error code: proxy: read response failed
Date Sat, 31 Oct 2009 15:55:16 GMT
we have one Apache-2.2.13 running mod_proxy_ajp + mod_proxy_balancer,
connected to (3) Tomcat-6.0.20 instances under Fedora release 8. We
are experiencing some issues with high CPU load on the Tomcat side,
and Apache starts logging errors like these

[Fri Oct 30 14:47:43 2009] [error] (70007)The timeout specified has
expired: ajp_ilink_receive() can't receive header
[Fri Oct 30 14:47:43 2009] [error] ajp_read_header: ajp_ilink_receive failed
[Fri Oct 30 14:47:43 2009] [error] (120006)APR does not understand
this error code: proxy: read response failed from

On Tomcat side we are using the APR Native Connector, with this settings:

 <Connector port="8009" protocol="AJP/1.3" redirectPort="8443"
maxThreads="130" backlog="10" connectionTimeout="30000"
keepAliveTimeout="30000" enableLookups="false" />

Apache MPM conf:

ServerLimit 100
<IfModule mpm_worker_module>
   StartServers         30
   MaxClients         2500
   MinSpareThreads      50
   MaxSpareThreads     100
   ThreadsPerChild      25
   MaxRequestsPerChild   0

mod_proxy_ajp conf:

<Proxy balancer://jogacraque>
   BalancerMember ajp:// route=app01 ttl=30 max=2
   BalancerMember ajp:// route=app02 ttl=30 max=2
   BalancerMember ajp:// route=app03 ttl=30 max=2

Apache specs:

Server version: Apache/2.2.13 (Unix)
Server built:   Sep 29 2009 11:12:35
Server's Module Magic Number: 20051115:23
Server loaded:  APR 1.3.8, APR-Util 1.3.9
Compiled using: APR 1.3.8, APR-Util 1.3.9
Architecture:   32-bit
Server MPM:     Worker
 threaded:     yes (fixed thread count)
 forked:     yes (variable process count)

I've beeng testing different settings for mod_proxy_ajp, but I am not
sure what is the exact relation between the max option for mod_proxy
and ThreadsPerChild. Should I set max to 1? I understand I would have
as many connections to each Tomcat box as
max*(MaxClients/ThreadsPerChild), is this correct?

BTW, is the total number of connections that mod_proxy_ajp will
forward to Tomcat related with MaxThreads ? I don't fully understand
how APR connector works in this case.

Thanks in advance,
-Damian Traverso

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