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javadockercontainersmemory-limitcgroups

How to prevent Java from exceeding the container memory limits?

I'm running a Java program inside a Docker container that has a hard memory limit of 4GB. I've set the max heap to 3GB but still the Java program exceeds the limit and gets killed (OOMKilled).

My question is: How can I configure Java to respect the set container limit and throw an OutOfMemoryException instead of trying to allocate beyond the limit and get its ass kicked by the host kernel?

Update: I'm an experienced Java developer and have a fair understanding of the JVM. I know how to set the max heap, but I wonder if anyone knows of a way to set a limit to the total memory that the JVM process claims from the OS.

Solution

  • When a Java application is executed inside a container, the JVM ergonomics (which is responsible for dynamically assign resources based on the host's capabilities) does not know it is running inside a container and it calculates the number of resources to be used by the Java app based on the host that is executing your container. Given that, it does not matter if you set limits to your container, the JVM will take your host's resources as the base for doing that calculation.

    From JDK 8u131+ and JDK 9, there’s an experimental VM option that allows the JVM ergonomics to read the memory values from CGgroups. To enable it you must pass the following flags to the JVM:

    -XX:+UnlockExperimentalVMOptions and -XX:+UseCGroupMemoryLimitForHeap

    If you enable these flags, the JVM will be aware that is running inside a container and will make the JVM ergonomics to calculate the app's resources based on the container limits and not the host's capabilities.

    Enabling the flags:

    $ java -XX:+UnlockExperimentalVMOptions -XX:+UseCGroupMemoryLimitForHeap -jar app.jar

    You can dynamically pass the JVM options to your container with ENV variables.

    Example:

    The command to run your app would like something like:

     $ java ${JAVA_OPTIONS} -jar app.jar

    And the docker run command needs to pass the ENV variable like this:

    $ docker run -e JAVA_OPTIONS="-XX:+UnlockExperimentalVMOptions -XX:+UseCGroupMemoryLimitForHeap" myJavaImage

    Hope this helps!