Java in a Container

External

• https://developers.redhat.com/blog/2017/03/14/java-inside-docker/
• https://blog.softwaremill.com/docker-support-in-new-java-8-finally-fd595df0ca54
• https://stackoverflow.com/questions/54292282/clarification-of-meaning-new-jvm-memory-parameters-initialrampercentage-and-minr/54297753#54297753

Internal

• Docker Container Best Practices
• Java Memory
• Kubernetes Resources Management Concepts
• Docker Resources Management Concepts

Overview

When running java in a container, the max heap should always be explicitly set with -Xmx, based on the application needs and the container limits.

Java max heap limit can also be calculated based on the container limits.

Generic script that correlates JVM memory settings to the container limits: https://github.com/fabric8io-images/run-java-sh, https://github.com/fabric8io-images/run-java-sh/blob/master/fish-pepper/run-java-sh/fp-files/run-java.sh.

Let JVM Adjust Memory Relative to CGroups Limits

Experimental Options

Java 1.8.0_181

(since Java 1.8.0_131)

java -XX:+UnlockExperimentalVMOptions  -XX:+UseCGroupMemoryLimitForHeap -XX:MaxRAMFraction=50 -XX:+PrintFlagsFinal -version | | grep MaxHeapSize

-XX:+UseCGroupMemoryLimitForHeap configures the JVM to read CGroups memory limit from /sys/fs/cgroup/memory/memory.limit_in_bytes and use it as a base when setting the max heap.

Java 1.8.0_221

java -XX:MaxRAMPercentage=20.0 -XX:+PrintFlagsFinal -version | grep MaxHeapSize

Other flags:

-XX:InitialRAMPercentage

-XX:MinRAMPercentage