Investigation into Java Garbage collection with Kubernetes CPU and memory limits

App.java

/**
 * Copyright (c) 2020 Mark Himsley
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */
package com.mdsh.jvm_options;

import java.io.IOException;
import java.lang.management.GarbageCollectorMXBean;
import java.lang.management.ManagementFactory;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Arrays;

import javax.management.InstanceNotFoundException;
import javax.management.MBeanException;
import javax.management.MalformedObjectNameException;
import javax.management.ObjectName;
import javax.management.ReflectionException;

public class App {

    public static void main(String[] args) throws InstanceNotFoundException, MalformedObjectNameException, ReflectionException, MBeanException, NullPointerException {
        
        // from the answer to:
        // https://stackoverflow.com/questions/54862460/how-to-determine-which-gc-i-use
        Object flags = ManagementFactory.getPlatformMBeanServer().invoke(
                ObjectName.getInstance("com.sun.management:type=DiagnosticCommand"),
                "vmFlags", new Object[] { null }, new String[] { "[Ljava.lang.String;" });
        System.out.println("vmFlags");
        for(String f: ((String)flags).split("\\s+")) {
            System.out.printf("  %s%n",f);
        }
        System.out.println("Garbage Collectors");
        for(GarbageCollectorMXBean gc: ManagementFactory.getGarbageCollectorMXBeans()) {
            System.out.printf("  %-45s: %s%n", gc.getName(), Arrays.toString(gc.getMemoryPoolNames()));
        }
        // walk through /sys/fs/ directories getting interesting information
        printSYSFSValues(Path.of("/sys/fs/cgroup/cpu/"), "cpu.");
        printSYSFSValues(Path.of("/sys/fs/cgroup/memory/"), "memory.");
    }

    private static void printSYSFSValues(Path path, String match) {
        System.out.println("contents of " + path.toString() + "/" + match + "*");
        if (path.toFile().exists() && path.toFile().canRead()) {
            for (String file : path.toFile().list()) {
                if (!file.startsWith(match)) {
                    continue;
                }
                Path p = path.resolve(file);
                if (p.toFile().canRead()) {
                    try {
                        String content = Files.readString(p, StandardCharsets.US_ASCII);
                        System.out.printf("  %-45s: %s", p.toString(), content);
                    } catch (IOException e) {
                        System.out.printf("  %-45s: <could not read contents>%n", p.toString());
                    }
                }
            }
        }
    }
}

Dockerfile

FROM openjdk:11-jre
WORKDIR /opt/mdsh
COPY jvmoptions.jar lib/
CMD ["sh", "-c", "java $JAVA_OPTS -Dfile.encoding=UTF-8 -Duser.timezone=UTC -jar lib/jvmoptions.jar"]