[users@httpd] Connection errors with mod_proxy_balancer and tomcat 5.5

[Peter Buning <bu...@kicktipp.de>]

Hi,

we encounter some strange errors with our apache (v2.2)  fronting 4 tomcat 
(v5.5) server. 

We are loadbalancing with sticky sessions to our tomcats. Everything runs fine 
beside the fact that 0.1% of all requests get a 503 http status code. The rate 
raises under load, but it is at least 0.1% (way too much!!) and occurs even at 
the early morning hours. The request is not logged on the tomcat side (no 
exceptions, no access.log), only on apache access.log with 503 and error log 
as stated below.

1. This is from our apache log file:

[Wed Mar 25 07:08:44 2009] [error] [client 74.6.22.94] (70014)End of file 
found: proxy: error reading status line from remote server tc1 
[Wed Mar 25 07:08:44 2009] [error] [client 74.6.22.94] proxy: Error reading 
from remote server returned by /site.html

2. This is from our apache config  (prefork engine)

KeepAlive Off

ServerLimit           650
ListenBackLog          50
StartServers           50
MinSpareServers       100
MaxSpareServers       200
MaxClients            300
MaxRequestsPerChild 10000

ProxyRequests Off

<Proxy balancer://tomcatcluster>
  BalancerMember http://tc1:80 max=100 route=tc1
  BalancerMember http://tc2:80 max=100 route=tc2
  BalancerMember http://tc3:80 max=100 route=tc3
  BalancerMember http://tc4:80 max=100 route=tc4
  Order Deny,Allow
  Allow from all
</Proxy>

ProxyPass / balancer://tomcatcluster/ stickysession=JSESSIONID|jsessionid
ProxyPassReverse / http://tc1/
ProxyPassReverse / http://tc2/
ProxyPassReverse / http://tc3/
ProxyPassReverse / http://tc4/
ProxyPreserveHost On

3. This is our connector from our tomcat configuration
<Connector 
   port="80" URIEncoding="UTF-8" maxHttpHeaderSize="8192" 
   maxThreads="200" minSpareThreads="100" maxSpareThreads="200"
   enableLookups="false" acceptCount="25" 
   connectionTimeout="10000" disableUploadTimeout="true" 
   maxKeepAliveRequests="100"
   compression="on" compressionMinSize="2048"
   noCompressionUserAgents="gozilla, traviata" 
   compressableMimeType="text/html,text/xml,text/css"
/>

I tried to investigate this problem but wasn't even able to reproduce it on my 
test engine. Googling it, i found some other people having this problem but no 
solution.

As far as i understand from my investigations "BalancerMember http://tc1:80 
max=100" does not make sense on "prefork". max should be 1 with prefork model. 
But i think this is not the reason. 

if max=100 is not effective, there "could" be situations where MaxClients of 
300 all go to one tomcat because of session affinity. But this is rather 
theoretical.

Maybe i can't use keepalive on the tomcat side. But it seems to work. But 
honestly: i am clueless.

Do you have any hints why i do encounter these connection errors?

Or does anybody has a running configuration with apache2.2, mod_proxy_balancer 
and tomcat 5.5. where these problems does not occur? 

kind regards
Peter



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