Getting 502 errors in isapi_redirect.log (ColdFusion 11)

Question

Hello,
We have browsed many threads on the subject of tuning CF11 (& CF10) IIS connectors (in particular ColdFusion 10 instance/Tomcat dying at predictable intervals (white screen of death) )
and we have applied the suggested changes to tune the connector.
workers.properties:
     worker.cfusion.max_reuse_connections=250
     worker.cfusion.connection_pool_timeout = 60
     worker.cfusion.connection_pool_size=250
server.xml
     <Connector port="8014" protocol="AJP/1.3" redirectPort="8447" tomcatAuthentication="false" maxThreads="250" connectionTimeout="60000" />
The above has fixed the issues/failures we had under load (503 errors, white screens).
But now we are getting 502 errors in the isapi_redirect.log as follows:
[Mon Dec 01 18:35:53.717 2014] [20632:12484] [info] ajp_connection_tcp_get_message::jk_ajp_common.c (1308): (cfusion) can't receive the response header message from tomcat, tomcat (127.0.0.1:8014) has forced a connection close for socket 1088
[Mon Dec 01 18:35:53.717 2014] [20632:12484] [error] ajp_get_reply::jk_ajp_common.c (2260): (cfusion) Tomcat is down or network problems. Part of the response has already been sent to the client
[Mon Dec 01 18:35:53.717 2014] [20632:12484] [error] ajp_service::jk_ajp_common.c (2735): (cfusion) sending request to tomcat failed (unrecoverable),  (attempt=1)
[Mon Dec 01 18:35:53.717 2014] [20632:12484] [error] HttpExtensionProc::jk_isapi_plugin.c (2612): service() failed with http error 502
These are popping up once every minute or so. But the site is running ok.
The log file is growing (obviously) and I would appreciate help on how to diagnose these errors (and whether these are worrying or not...)
Thanks.

Answer 1

Regarding AJP APR.
If you open CF10 CF11 coldfusion-error.log you will notice something like EG:
org.apache.catalina.core.AprLifecycleListener init
INFO: The APR based Apache Tomcat Native library which allows optimal
performance in production environments was not found on the java.library.path etc
org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["ajp-bio-8012"]
Some cut and pasting from tomcat doc you can read full detail from here:
http://tomcat.apache.org/native-doc/index.html
The Apache Tomcat Native Library  provides portable API for features not found in contemporary JDK's. It uses Apache Portable Runtime (APR) as operating system abstraction layer and allows optimal performance in production environments.
How to change CF from BIO to APR?
-Download tomcat native http://tomcat.apache.org/download-native.cgi windows binaries
-extract tcnative-1.dll to CF10 CF11 \cfusion\lib
-Note tcnative-1.dll in \bin\x64 for 64bit source versa 32bit
-Restart CF10 CF11 application service
Outcome coldfusion-error.log now says EG:
INFO: Loaded APR based Apache Tomcat Native library 1.1.32.
org.apache.catalina.core.AprLifecycleListener init
etc
org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["ajp-apr-8012"]
Post again if that helps with the 502 error message or not. Probably will not assist tribule's thread since I have seen same ISAPI log details with APR present.
Regards, Carl.