The document discusses Java's integration with container environments, highlighting how to leverage container features such as CPU and memory boundaries. It also introduces solutions like Application Class Data Sharing (AppCDS) and Ahead-Of-Time (AOT) compilation to optimize Java applications in containers. Additionally, it emphasizes the importance of following best practices for containerizing Java applications and provides resources and contact information for further inquiries.

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Java for the containers
Vaibhav Choudhary (@vaibhav_c)
Java Platforms Team
https://blogs.oracle.com/vaibhav

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The following is intended to outline our general product direction. It is intended
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is not a commitment to deliver any material, code, or functionality, and should
not be relied upon in making purchasing decisions. The development, release,
and timing of any features or functionality described for Oracle’s products
remains at the sole discretion of Oracle.
3

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Agenda of the day …
A brief on Container
Java - as first class citizen in Container
Respect Container Boundary
Leverage features inside container
Final thoughts
1
2
3
4
4
5

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Respective the container Boundary

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Processor Boundary (--cpu-shares)
6
public class CoreCheck {
public static void main(String[] args) {
System.out.println(Runtime.getRuntime().availableProcessors());
}}
JDK8 :
docker run --rm --cpu-shares 2048 -v /root/:/mnt/mydata -it ubuntu bash
root@7599aae2613d:/mnt/mydata/jdk-8/bin# ./java CoreCheck
8
FROM openjdk:10
ADD CoreCheck.java .
WORKDIR .
RUN javac CoreCheck.java
CMD ["java", "CoreCheck" ]
docker build -t hello-world .
docker run --cpu-shares 2048 java-helloworld
2

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Processor Boundary (--cpuset-cpus)
7
public class CoreCheck {
public static void main(String[] args) {
System.out.println(Runtime.getRuntime().availableProcessors());
}}
JDK8 :
docker run --rm --cpuset-cpus 3,4,6 -v /root/:/mnt/mydata -it ubuntu bash
root@7599aae2613d:/mnt/mydata/jdk-8/bin# ./java CoreCheck
8 (ideally it should say 3)
FROM openjdk:10
ADD CoreCheck.java .
WORKDIR .
RUN javac CoreCheck.java
CMD ["java", "CoreCheck" ]
docker build -t hello-world .
docker run --cpuset-cpus 3,4,6 java-
helloworld
3 (Processor 3rd, 4th and 6th)

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Here are the results (Respecting Logs)
8
public class HelloWorld {
public static void main(String[] args) {
System.out.println(Runtime.getRuntime().availableProcessors());
}}
JDK10 :
root@4795a54e037e:/mnt/mydata/jdk-10b38/bin# ./java -Xlog:os+container=trace HelloWorld
[0.001s][trace][os,container] OSContainer::init: Initializing Container Support
[0.001s][trace][os,container] Path to /memory.limit_in_bytes is /sys/fs/cgroup/memory/
memory.limit_in_bytes
JDK9 :
root@4795a54e037e:/mnt/mydata/jdk-9/bin# ./java -Xlog:os+container=trace HelloWorld
[0.001s][error][logging] Invalid tag 'container' in what-expression.
Invalid -Xlog option '-Xlog:os+container=trace'

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Here are the results (ActiveProcessorCount)
9
public class HelloWorld {
public static void main(String[] args) {
System.out.println(Runtime.getRuntime().availableProcessors());
}}
JDK10 :
root@4795a54e037e:/mnt/mydata/jdk-10b38/bin# ./java -
XX:ActiveProcessorCount=4 HelloWorld
4
JDK8 :
root@4795a54e037e:/mnt/mydata/jdk1.8.0_152/bin# ./java -
XX:ActiveProcessorCount=4 HelloWorld
Unrecognized VM option 'ActiveProcessorCount=4'
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.

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Cont.. (Respecting Memory Boundaries)
10
public class MemoryCheck {
public static void main(String[] args) {
System.out.println(Runtime.getRuntime().maxMemory());
}}
JDK8 :
docker run --rm --memory 100m -v /root/:/mnt/mydata -it ubuntu bash
root@7599aae2613d:/mnt/mydata/jdk-8/bin# ./java CoreCheck
It will print 1/4 of the Physical Memory (It should understand docker memory limit)
FROM openjdk:10
ADD MemoryCheck.java .
WORKDIR .
RUN javac MemoryCheck.java
CMD ["java", "MemoryCheck" ]
docker build -t hello-world .
docker run --memory 100m java-helloworld
Half of the docker limit (50m)

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Solution 1 : Application Class Data Sharing (AppCDS)

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How Application Class Data Sharing (AppCDS) Help?
• CDS only supports archiving classes on the bootstrap class path, which provides
limited (or no) benefit for large applications in today’s cloud environment as
majority of loaded classes are application classes.
• AppCDS extends the archiving support beyond core library classes
– Enables archiving classes loaded by all class loaders
• PlatformClassLoader (the ExtensionClassLoader in JDK 8 and earlier versions)
• AppClassLoader
• User defined class loaders
• AppCDS allows archiving and sharing read-only java heap objects with G1 GC
• AppCDS provides further reduction in storage for archived class metadata
12

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A Quick Look at CDS/AppCDS Evolution
13
JDK 1.5 JDK 8 JDK 9JDK8u40
CDS AppCDS v1
(experimental)
AppCDS v2
(experimental)
Cache classes from
boot loader only
Cache classes from built-in class loaders
Boot, Extension and App class loaders
Cache classes from built-in and
user defined class loaders

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AppCDS Architectural View
14
JVM Instance 1 JVM Instance 1
Java Heap
Space
Shared Space
Meta Space
Heap Objects
Class Metadata
Shared String Objects
Class Metadata
Archive
File
Shared Classes
Heap Objects
Shared String Objects
Shared Classes

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• About 30% startup time
improvement observed
with AppCDS for Oracle
Web Logic Server (WLS)
base domain
15
Startup Time Improvements for Oracle Web Logic Server
0s
2.875s
5.75s
8.625s
11.5s
WLS BaseDomain
7.7s
11.4s
No AppCDS AppCDS

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AppCDS inside Container - How to use
• Simple CDS use in Docker
DockerFile
FROM openjdk:10
ADD HelloWorld.java .
WORKDIR .
RUN javac HelloWorld.java
RUN ["java", "-Xshare:dump" ]
CMD ["java", "-showversion" , "-Xshare:on", "HelloWorld" ]

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Cont…
• Determine the class to archive
java -Xshare:off -XX:+UseAppCDS -XX:DumpLoadedClassList=hello.lst -cp hello.jar
HelloWorld
• Creating the AppCDS archive
java -Xshare:dump -XX:+UseAppCDS -XX:SharedClassListFile=hello.lst
-XX:SharedArchiveFile=hello.jsa -cp hello.jar
• Using the AppCDS archive
java -Xshare:on -XX:+UseAppCDS -XX:SharedArchiveFile=hello.jsa
-cp hello.jar HelloWorld

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Solution 2: Ahead of Time Compilation (AOT)

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At Compile Time At Runtime Time
Java Source [*.java]
Java Bytecode [*.class]
javac
Classloader
Verifier
Java
Interpreter
JIT
Compiler
(C1, C2)
Native Level (OS,
Hardware)
Most of the
code get
optimized
here
Shared Object [*.so]
jaotc

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• jaotc --output HelloWorld.so HelloWorld.class
• java -XX:AOTLibrary=./HelloWorld.so HelloWorld
20
-bash-4.1$ ./java -XX:+PrintAOT -XX:AOTLibrary=./HelloWorld.so
HelloWorld
15 1 loaded ./HelloWorld.so aot library
153 1 aot[ 1] HelloWorld.<init>()V
153 2 aot[ 1] HelloWorld.main([Ljava/lang/String;)V
Hello AOT
• jaotc --output base.so --module java.base

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AOT run (jaotc)
21
-bash-4.1$ ./jaotc --info --output HelloWorld.so HelloWorld.class
Compiling HelloWorld...
1 classes found (62 ms)
2 methods total, 2 methods to compile (6 ms)
Compiling with 2 threads
.
2 methods compiled, 0 methods failed (923 ms)
Parsing compiled code (2 ms)
Processing metadata (21 ms)
Preparing stubs binary (1 ms)
Preparing compiled binary (0 ms)
Creating binary: HelloWorld.o (17 ms)
Creating shared library: HelloWorld.so (26 ms)
Total time: 1886 ms

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Dynamic (JIT) Static (AOT)
Start-up performance Tunable, but not so good Best
Steady-state performance Best Good
Interactive performance Not so good Good
Deterministic performance Tunable, but not best Best
* https://www.ibm.com/developerworks/library/j-rtj2/index.html

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* https://www.ibm.com/developerworks/library/j-rtj2/index.html

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Solution 3: Modularity

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DockerFile should look like
FROM openjdk:10 as small
ADD jdk-10.tar.gz /jdk
ENV PATH=$PATH:/jdk/jdk-10/bin
RUN [“jlink”, “—compress=2”, “—module-path”, “/jdk/jdk-10/jmods”,
“—add-modules”, “java.base”, “—output”, “/linked” ]
FROM openjdk:10
COPY —from=small /linked /jdk
ADD HelloWorld.class
CMD [“java”, “-showversion”, “HelloWorld”]

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Links
• For any query, you can drop me mail at vaibhav.x.choudhary@oracle.com
• Good links :-
• Bangalore JUG resource - http://bangalorejug.org/downloads/
• Container Aware Java - http://openjdk.java.net/jeps/8182070
• JDK-8146115 - https://bugs.openjdk.java.net/browse/JDK-8146115
• Better containerization by JDK10 : https://mjg123.github.io/
2018/01/10/Java-in-containers-jdk10.html
• VJUG Talk :- Java in Container world