mod_jk 如何处理节点故障

Question

We have configured mod_jk with two tomcat servers with 2 apache web servers. We wanted to know how mod_jk handling node failure or how it will do a health check.?

Answer 1

You can use a watchdog by setting the JkWatchdogInterval directive. From the documentation :

This directive configures the watchdog thread interval in seconds. The workers are maintained periodically by a background thread running periodically every watchdog_interval seconds. Worker maintenance checks for idle connections, corrects load status and is able to detect backend health status. The maintenance only happens, if since the last maintenance at least worker.maintain seconds have passed. So setting the JkWatchdogInterval much smaller than worker.maintain is not useful.

The default value is 0 seconds, meaning the watchdog thread will not be created, and the maintenance is done in combination with normal requests instead.

Answer 2

In Advanced Worker Directives, use "redirect", this will Set to the name of the preferred failover worker. Eg : worker.server-four.redirect=server-two

If worker matching SESSION ID is in error state then the redirect worker will be used instead.

This feature has been added in jk 1.2.9.

Status of mod_jk

Please add the below tag in mod_jk.conf file

JkMount status Order deny,allow Deny from all Allow from 127.0.0.1

Then you can find the status of mod_jk by using below URL

http://webserverIP:port(from httpd.conf)/status