Tomcat 7.0.47 running on Linux
I have started investigating after noticing following messages from
"dmesg" output on a production server.
"possible SYN flooding on port 28080. Sending cookies."
Started looking into this as the connections to this server are timing
out (Connect Timeout errors). Upon further investigation, it appears to
me that Linux's kernel maintain two different queues one for SYN and one
for ESTABLISHED/accept connections. Both are determined by following
parameters.
$ cat /proc/sys/net/ipv4/tcp_max_syn_backlog
2048
$ cat /proc/sys/net/core/somaxconn
128
Also, it appears that the second parameter (accept count) is determined
by the application. For tomcat it defaults to 100. As per this document
- http://blog.dubbelboer.com/2012/04/09/syn-cookies.html above two
parameters could be tuned to increase the accepted connections.
Wondering if Tomcat's "acceptCount"
(http://tomcat.apache.org/tomcat-7.0-doc/config/http.html) parameter is
related to "somaxconn" for tuning.
Thanks in advance for your comments.
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