Guide using Jshell to query CPU and memory information within a docker container #jvm #guide #complete

jshell_docker_snippets.sh

#!/usr/bin/env bash


# Ref: https://jaxenter.com/better-containerized-jvms-jdk-10-140593.html

set -eu

OPENJDK_IMAGE='openjdk:10-ea-jdk-slim'

JSHELL_CMD=(/bin/sh -c 'jshell -q')
GREP_CMD="-e HeapSize -e '\<ThreadStackSize\>' -e '\<ConcGCThreads\>' -e '\<ParallelGCThreads\>'"
JAVA_CMD=(/bin/sh -c "java -XX:+PrintFlagsFinal -version 2>/dev/null | grep -i ${GREP_CMD}")

JSHELL_EXIT_SEQUENCE='\n\\exit'

# List the final flags
echo "List the final flags"
sleep 1

echo "${JAVA_CMD[@]}"
docker run "${OPENJDK_IMAGE}" "${JAVA_CMD[@]}"
echo
echo
sleep 1

# List the number of processors on the host
echo "List the number of processors on the host"
sleep 1

printf "Runtime.getRuntime().availableProcessors()" \
  | xargs -0 printf "%s${JSHELL_EXIT_SEQUENCE}" \
  | "${JSHELL_CMD[@]}"
echo
echo
sleep 1

# jshell> Runtime.getRuntime().availableProcessors()
# $1 ==> 8
# jshell> \exit%

# List the number of processors within the container
echo "List the number of processors within the container"
sleep 1

printf "Runtime.getRuntime().availableProcessors()" \
  | xargs -0 printf "%s${JSHELL_EXIT_SEQUENCE}" \
  | docker run -i "${OPENJDK_IMAGE}" "${JSHELL_CMD[@]}"
echo
echo
sleep 1

# Mar 24, 2018 8:55:40 PM java.util.prefs.FileSystemPreferences$1 run
# INFO: Created user preferences directory.
# jshell> Runtime.getRuntime().availableProcessors()
# $1 ==> 8
# jshell> \exit%  

## CPU Shares

# From: https://jaxenter.com/better-containerized-jvms-jdk-10-140593.html#cpu-shares
#
# This rations the CPU according to the proportions you choose, but only when
# the system is busy. For example, you can have three containers with shares of
# 1024/512/512, but those limits are only applied when necessary. When there is
# headroom your containerized process can use left-over CPU time.

# 1 CPU = 1024 shares, so 36864/1024 = 36 processors, however 36 > 8, so 8 is reported
echo "List the number of processors within the container with 36864 cpu shares"
sleep 1

printf "Runtime.getRuntime().availableProcessors()" \
  | xargs -0 printf "%s${JSHELL_EXIT_SEQUENCE}" \
  | docker run --cpu-shares 36864 -i "${OPENJDK_IMAGE}" "${JSHELL_CMD[@]}"
echo
echo
sleep 1

# Mar 24, 2018 8:58:55 PM java.util.prefs.FileSystemPreferences$1 run
# INFO: Created user preferences directory.
# jshell> Runtime.getRuntime().availableProcessors()
# $1 ==> 8
# jshell> \exit% 

# 1 CPU = 1024 shares, so 4096/1024 = 4 processors, since 4 < 8, 4 is reported
echo "List the number of processors within the container with 4096 cpu shares"
sleep 1

printf "Runtime.getRuntime().availableProcessors()" \
  | xargs -0 printf "%s${JSHELL_EXIT_SEQUENCE}" \
  | docker run --cpu-shares 4096 -i "${OPENJDK_IMAGE}" "${JSHELL_CMD[@]}"
echo
echo
sleep 1

# Mar 24, 2018 9:02:19 PM java.util.prefs.FileSystemPreferences$1 run
# INFO: Created user preferences directory.
# jshell> Runtime.getRuntime().availableProcessors()
# $1 ==> 4
# jshell> \exit%   

## CPU Quota

# From: https://jaxenter.com/better-containerized-jvms-jdk-10-140593.html#cpu-periodquota
#
# This uses the Linux Completely Fair Scheduler to limit the container’s CPU
# usage. This means that the container will have limited CPU time even when the
# machine is lightly loaded and your workload may be spread across all the CPUs
# on the host. The example here might give you 50% time on all 72 cores, for
# example.

# TODO:
# /nix/store/aiahnd4gqvlv0hlgs4j3sv91x8zy05zg-docker-17.09.1-ce/libexec/docker/docker:
# Error response from daemon: NanoCPUs can not be set, as your kernel does not
# support CPU cfs period/quota or the cgroup is not mounted.
#
# See: https://github.com/moby/moby/issues/12348
# See:

# echo "List the number of processors within the container with 2 cpus"
# sleep 1

# printf "Runtime.getRuntime().availableProcessors()" \
#   | xargs -0 printf "%s${JSHELL_EXIT_SEQUENCE}" \
#   | docker run --cpus 2 -i "${OPENJDK_IMAGE}" "${JSHELL_CMD[@]}"
# echo
# sleep 1

## CPU Sets

# From: https://jaxenter.com/better-containerized-jvms-jdk-10-140593.html#cpu-sets
#
# Unlike the two previous constraints, this pins the containerized process to
# specific CPUs. Your process may have to share those CPUs, but will obviously
# not be allowed to use spare capacity on any others.

echo "List the number of processors within the container with cpuset of 0-2 (3 total) cpus"
sleep 1

printf "Runtime.getRuntime().availableProcessors()" \
  | xargs -0 printf "%s${JSHELL_EXIT_SEQUENCE}" \
  | docker run --cpuset-cpus 0-2 -i "${OPENJDK_IMAGE}" "${JSHELL_CMD[@]}"
echo
echo
sleep 1

# Mar 24, 2018 9:10:01 PM java.util.prefs.FileSystemPreferences$1 run
# INFO: Created user preferences directory.
# jshell> Runtime.getRuntime().availableProcessors()
# $1 ==> 3
# jshell> \exit%

## Memory

# List the memory on the host
echo "List the memory on the host"
sleep 1

printf "Runtime.getRuntime().maxMemory()" \
  | xargs -0 printf "%s${JSHELL_EXIT_SEQUENCE}" \
  | "${JSHELL_CMD[@]}"
echo
echo
sleep 1

# jshell> Runtime.getRuntime().maxMemory()
# $1 ==> 2048917504
# jshell> \exit% 

# List the memory within the container
echo "List the mex memory within the container"
sleep 1

printf "Runtime.getRuntime().maxMemory()" \
  | xargs -0 printf "%s${JSHELL_EXIT_SEQUENCE}" \
  | docker run -i "${OPENJDK_IMAGE}" "${JSHELL_CMD[@]}"
echo
echo
sleep 1

# Mar 24, 2018 9:14:11 PM java.util.prefs.FileSystemPreferences$1 run
# INFO: Created user preferences directory.
# jshell> Runtime.getRuntime().maxMemory()
# $1 ==> 2048917504
# jshell> \exit%