My application setup: 4 docker containers setup by docker-compose: myapplication (tomcat, jersey application), kafka, postgres, zookeeper.
I need to know the CPU usage of tomcat container.
1, I used JavaMeloday to get % System CPU 93.36, more details.
2, I used docker stats <docker id> to get that CPU % is 356% at the same time with % System CPU 93.36 by JavaMelody.
In my machine, there are 8 cores. why the numbers in 1 and 2 are different? How to explain them?
Thanks
As mentioned in moby/moby issue 26711:
800% is correct here, which is a standard notation for telling that 8 cores are 100% in use.
So 356% means the docker container processes (not just the java Tomcat) uses almost 4 of the 8 cores.
As opposed to Javamelody, used in "A Step-by-Step Guide to Tomcat Performance Monitoring", which monitors the Java application through JMX, and reports more: from "Java – monitoring cpu and system load of multi-threaded application via OperatingSystemMXBean", that value is an aggregate for all cores).
The issue is: docker stats and javamelody don't monitor the activity at exactly the same time, and could report (and aggregate) different activity peaks.