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From Shantanu Pavgi <>
Subject Re: [users@httpd] http-tomcat - AJP ilink receive failed - 500/503 errors
Date Fri, 17 Sep 2010 18:14:08 GMT

Thanks for the reply Martin.

Telnet works, but it's difficult to say as sometimes AJP also works. I don't need to restart
any of the services to resolve this problem. It starts working back again on it's own after
few seconds/minutes for future requests. It's random error (until the real trigger is found).


On Sep 17, 2010, at 12:07 PM, Martin Hasicek wrote:


you should try to telnet tomcat server from web server.

telnet <host> <port>

If the telnet is successful, you need to check configuration of mod_proxy_ajp. If the telnet
will be not successful, you have network problem.


Sent from my iPhone

On 17.9.2010, at 18:18, Shantanu Pavgi <<>> wrote:


I have a Apache http server and a Tomcat server configured using AJP connector (mod_proxy_ajp).
The http server serves HTML/PHP pages and also proxies Java webapp requests to back-end Tomcat
System config:
* Both servers are running as Virtual Machines
* CentOS 5.4
* Apache Tomcat 6.0.26 and Sun JDK 1.6
* Apache http: 2.2.3 (it's old, but that's what comes with default CentOS repo)

We are getting HTTP 500/503 errors quite frequently, but they appear to be random in nature
and hence difficult to debug. I have tried increasing following config parameters, but it
didn't help:
* On http server: max and smax connections in proxy_ajp.conf
* On Tomcat server: maxThreads and maxSpareThreads in Tomcat's server.xml

Following logs were seen on both sides:
== Apache http server ==
* In browser: 500/503 - internal server error.
* In Apache logs at debug mode - same logs for 500 and 503 error:
[Wed Sep 15 22:50:09 2010] [debug] ajp_header.c(430): ajp_marshal_into_msgb: Done
[Wed Sep 15 22:50:09 2010] [debug] mod_proxy_ajp.c(239): proxy: APR_BUCKET_IS_EOS
[Wed Sep 15 22:50:09 2010] [debug] mod_proxy_ajp.c(244): proxy: data to read (max 8186 at
[Wed Sep 15 22:50:09 2010] [debug] mod_proxy_ajp.c(259): proxy: got 0 bytes of data
[Wed Sep 15 22:50:09 2010] [error] ajp_read_header: ajp_ilink_receive failed
[Wed Sep 15 22:50:09 2010] [error] (120006)APR does not understand this error code: proxy:
read response failed from (<><>)
[Wed Sep 15 22:50:09 2010] [debug] proxy_util.c(2062): proxy: AJP: has released connection
for (<><>)
[Wed Sep 15 22:50:09 2010] [debug] ssl_engine_kernel.c(1765): OpenSSL: Write: SSL negotiation
finished successfully
[Wed Sep 15 22:50:09 2010] [info] [client] Connection closed to child 3 with standard
shutdown (server
* tcpdump on Apache http server: Shows a packet going out to Tomcat server

== Tomcat server ==
* In Tomcat logs catalina.out: No logs
* In Tomcat access logs catalina.out: No logs
* tcpdump on Tomcat: No incoming packet seen

The request doen't seem to reach Tomcat at all. I have checked syslog (/var/log/messages),
but I don't see any dropped packet logs as well.

Anyone else had this issues before? Any pointers on how to debugs this would be really helpful.

Shantanu Pavgi.

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