I am experiencing a periodic mod_jk failure which leads to a 503 site error. I can netstat to Tomcat on port 8009 during these failures, so I suspect that there is an issue with the apache => tomcat threads. I have yet to find a culprit thread in a Tomcat stack trace dump.
OS: Ubuntu 10.04
Web Server: Apache2
App Server: Tomcat6
Error from mod_jk.log:
ajp_connect_to_endpoint::jk_ajp_common(c) (922): Failed opening socket to (127.0.0.1:8009) (errno=111)
<Connector port="8009" protocol="AJP/1.3" redirectPort="8443" />