Tomcat Connections Getting Disconnected After Period of Inactivity

In some network environments, the firewall or router might terminate some connections after a period of inactivity.

However, this is not enabled by default:

# netstat -anpo | grep :80 tcp6       0      0 192.168.1.7:80      123.123.123.123:38123    ESTABLISHED 21345/java           off (0.00/0/0)

To prevent this, KeepAlive must be enabled in Tomcat. This is done by editing the Connector configuration in the server.xml file and adding the "socket.soKeepAlive" attribute.

<Connector port="8080" protocol="HTTP/1.1"               connectionTimeout="20000"               redirectPort="8443"                socket.soKeepAlive="true"         />

However, this alone may not be enough, because by default in some Linux distros, the default KeepAlive time is 2 hours, which means the first KeepAlive packet does not get sent until 2 hours later. For networks that disconnect idle connections within e.g. 15 minutes, this is too late. To reduce this to e.g. 5 minutes:

echo 300 > /proc/sys/net/ipv4/tcp_keepalive_time

Note: this change will not survive reboot. To make this change permanent the /etc/sysctl.conf needs to be edited.

After restarting Tomcat, the connection will look like this:

# netstat -anpo | grep :80 tcp6    0      0 192.168.1.7:80    123.123.123.123:38123   ESTABLISHED 21345/java      keepalive (82.52/0/0)

References:

• http://www.tldp.org/HOWTO/html_single/TCP-Keepalive-HOWTO/
• https://tomcat.apache.org/tomcat-8.0-doc/config/http.html