зеркало из https://github.com/docker/labs.git
Merge pull request #342 from PaulSandoz/master
Chapter for Docker and Java 9
This commit is contained in:
Mano Marks
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@ -68,11 +68,13 @@ NOTE: `--parallel` switch will not work for Docker Compose version prior to 1.12
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NOTE: For Linux, `docker-compose` and `docker` commands need `sudo` access. So prefix all commands with `sudo`.
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=== Other Software
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. Install https://git-scm.com//[git].
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. Install Docker Cloud CLI following the https://docs.docker.com/docker-cloud/installing-cli/[instructions].
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. Download Java IDE based upon your choice and install.
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.. https://netbeans.org/downloads/[NetBeans 8.2] (`"Java SE"` version)
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.. https://www.jetbrains.com/idea/download/[IntelliJ IDEA Community or Ultimate]
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.. http://www.eclipse.org/downloads/eclipse-packages/[Eclipse IDE for Java EE Developers]
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. Download https://maven.apache.org/download.cgi[Maven] and install.
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. Install Docker Cloud CLI following the https://docs.docker.com/docker-cloud/installing-cli/[instructions].
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. Download the OpenJDK build of http://download.java.net/java/GA/jdk9/9/binaries/openjdk-9_linux-x64_bin.tar.gz/[JDK 9 for Linux x64].
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(See also the http://jdk.java.net/9/[OpenJDK JDK 9 download page].)
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. Download the early-access Open JDK build of http://jdk.java.net/9/ea[JDK 9 for Alpine Linux].
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@ -0,0 +1,327 @@
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:imagesdir: images
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== Build a Docker Image with JDK 9
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*PURPOSE*: This chapter explains how to create a Docker image with JDK 9.
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The prior chapter explained how, in general, to build a Docker image with Java.
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This chapter expands on this topic and focuses on JDK 9 features.
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=== Create a Docker Image using JDK 9
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Create a new directory, for example `docker-jdk9`.
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In that directory, create a new text file `jdk-9-debian-slim.Dockerfile`.
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Use the following contents:
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[source, text]
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----
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# A JDK 9 with Debian slim
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FROM debian:stable-slim
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# Download from http://jdk.java.net/9/
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# ADD http://download.java.net/java/GA/jdk9/9/binaries/openjdk-9_linux-x64_bin.tar.gz
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ADD openjdk-9_linux-x64_bin.tar.gz /opt
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# Set up env variables
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ENV JAVA_HOME=/opt/jdk-9
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ENV PATH=$PATH:$JAVA_HOME/bin
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CMD ["jshell", "-J-XX:+UnlockExperimentalVMOptions", \
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"-J-XX:+UseCGroupMemoryLimitForHeap", \
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"-R-XX:+UnlockExperimentalVMOptions", \
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"-R-XX:+UseCGroupMemoryLimitForHeap"]
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----
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This image uses `debian` slim as the base image and installs the OpenJDK build
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of JDK for linux x64 (see the setup section for how to download this into the
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current directory).
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The image is configured by default to run `jshell` the Java REPL. The
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experimental flag `-XX:+UseCGroupMemoryLimitForHeap` is passed to the REPL
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process (the frontend Java process managing user input and the backend Java
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process managing compilation). This option will ensure container memory
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constraints are honored.
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Build the image using the command:
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docker build -t jdk-9-debian-slim -f jdk-9-debian-slim.Dockerfile .
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List the images available using `docker image ls`:
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[source, text]
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----
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REPOSITORY TAG IMAGE ID CREATED SIZE
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jdk-9-debian-slim latest 023f6999d94a 4 hours ago 400MB
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debian stable-slim d30525fb4ed2 4 days ago 55.3MB
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----
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Other images may be shown as well but we are interested in these two images for
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now. The large difference in size is attributed to JDK 9, which is larger
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in size than JDK 8 because it also explicitly provides Java modules that we
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shall see more of later on in this chapter.
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Run the container using the command:
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docker container run -m=200M -it --rm jdk-9-debian-slim
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to see the output:
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[source, text]
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----
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INFO: Created user preferences directory.
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| Welcome to JShell -- Version 9
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| For an introduction type: /help intro
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jshell>
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----
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Query the available memory of the Java process by typing the following
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expression into the Java REPL:
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Runtime.getRuntime().maxMemory() / (1 << 20)
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to see the output:
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[source, text]
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----
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jshell> Runtime.getRuntime().maxMemory() / (1 << 20)
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$1 ==> 100
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----
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Notice that the Java process is honoring memory constraints (see the `--memory`
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of `docker run`) and will not allocate memory beyond that specified for the
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container.
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In a future release of the JDK it will no longer be necessary to specify an
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experimental flag (`-XX:+UnlockExperimentalVMOptions`) once the mechanism by
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which memory constraints are efficiently detected is stable.
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JDK 9 supports the set CPUs constraint (see the `----cpuset-cpus` of
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`docker run`) but does not currently support other CPU constraints such as
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CPU shares. This is ongoing work http://openjdk.java.net/jeps/8182070[tracked]
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in the OpenJDK project.
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Note: the support for CPU sets and memory constraints have also been backported
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to JDK 8 release 8u131 and above.
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To list all the Java modules distributed with JDK 9 run the following command:
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docker container run -m=200M -it --rm jdk-9-debian-slim java --list-modules
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In total there should be 75 modules:
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[source, text]
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----
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$ docker container run -m=200M -it --rm jdk-9-debian-slim java --list-modules | wc -l
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75
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----
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=== Create a Docker Image using JDK 9 and Alpine Linux
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Instead of `debian` as the base image it is possible to use Alpine Linux
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with an early access build of JDK 9 that is compatible with the muslc library
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shipped with Alpine Linux.
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Create a new text file `jdk-9-alpine.Dockerfile`.
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Use the following contents:
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[source, text]
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----
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# A JDK 9 with Alpine Linux
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FROM alpine:3.6
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# Add the musl-based JDK 9 distribution
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RUN mkdir /opt
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# Download from http://jdk.java.net/9/
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# ADD http://download.java.net/java/jdk9-alpine/archive/181/binaries/jdk-9-ea+181_linux-x64-musl_bin.tar.gz
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ADD jdk-9-ea+181_linux-x64-musl_bin.tar.gz /opt
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# Set up env variables
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ENV JAVA_HOME=/opt/jdk-9
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ENV PATH=$PATH:$JAVA_HOME/bin
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CMD ["jshell", "-J-XX:+UnlockExperimentalVMOptions", \
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"-J-XX:+UseCGroupMemoryLimitForHeap", \
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"-R-XX:+UnlockExperimentalVMOptions", \
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"-R-XX:+UseCGroupMemoryLimitForHeap"]
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----
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This image uses `alpine` 3.6 as the base image and installs the OpenJDK build
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of JDK for Alpine Linux x64 (see the link:ch01-setup.adoc[Setup Environments]
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chapter for how to download this into the current directory).
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The image is configured in the same manner as for the `debian`-based image.
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Build the image using the command:
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docker build -t jdk-9-alpine -f jdk-9-alpine.Dockerfile .
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List the images available using `docker image ls`:
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[source, text]
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----
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REPOSITORY TAG IMAGE ID CREATED SIZE
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jdk-9-debian-slim latest 023f6999d94a 4 hours ago 400MB
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jdk-9-alpine latest f5a57382f240 4 hours ago 356MB
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debian stable-slim d30525fb4ed2 4 days ago 55.3MB
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alpine 3.6 7328f6f8b418 3 months ago 3.97MB
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----
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Notice the difference in image sizes. Alpine Linux by design has been carefully
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crafted to produce a minimal running OS image. A cost of such a design is
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an alternative standard library https://www.musl-libc.org/[musl libc] that is
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not compatible with the C standard library (libc). As a result the JDK requires
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modifications to run on Alpine Linux. Such modifications have been proposed
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by the OpenJDK http://openjdk.java.net/projects/portola/[Portola Project].
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=== Create a Docker Image using JDK 9 and a Java application
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Clone the GitHib project https://github.com/PaulSandoz/helloworld-java-9 that
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contains a simple Java 9-based project:
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git clone https://github.com/PaulSandoz/helloworld-java-9.git
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(If you have a github account you may wish to fork it and then clone the fork
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so you can make modifications.)
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Enter the directory `helloworld-java-9` and build the project from within a
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running Docker container with JDK 9 installed:
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docker run --volume $PWD:/helloworld-java-9 --workdir /helloworld-java-9 \
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-it --rm openjdk:9-jdk-slim \
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./mvnw package
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(If you have JDK 9 installed locally on the host system you can build directly
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with `./mvnw package`.)
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In this case we are using the `openjdk:9-jdk-slim` on Docker hub that has been
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configured to work with SSL certificates so that the maven wrapper tool can
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successfully download the maven tool. This image is not produced or in anyway
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endorsed by the OpenJDK project (unlike the JDK 9 distributions that were
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previously required). It is anticipated that future releases of the JDK from
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the OpenJDK project will have root CA certificates (see issue
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https://bugs.openjdk.java.net/browse/JDK-8189131[JDK-8189131])
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To build Docker image for this application create a new text file
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`helloworld-jdk-9.Dockerfile` with the following contents:
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[source, text]
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----
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# Hello world application with JDK 9 and Debian slim
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FROM jdk-9-debian-slim
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COPY target/helloworld-1.0-SNAPSHOT.jar /opt/helloworld/helloworld-1.0-SNAPSHOT.jar
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# Set up env variables
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CMD java -XX:+UnlockExperimentalVMOptions -XX:+UseCGroupMemoryLimitForHeap \
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-cp /opt/helloworld/helloworld-1.0-SNAPSHOT.jar org.examples.java.App
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----
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Build a Docker image containing the simple Java application based of the Docker
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image `jdk-9-debian-slim`:
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docker build -t helloworld-jdk-9 -f helloworld-jdk-9.Dockerfile .
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List the images available using `docker image ls`:
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[source, text]
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----
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REPOSITORY TAG IMAGE ID CREATED SIZE
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helloworld-jdk-9 latest eb0539e9529a 19 seconds ago 400MB
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jdk-9-debian-slim latest 023f6999d94a 5 hours ago 400MB
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jdk-9-alpine latest f5a57382f240 5 hours ago 356MB
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openjdk 9-jdk-slim 6dca67f4790e 3 days ago 372MB
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debian stable-slim d30525fb4ed2 4 days ago 55.3MB
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alpine 3.6 7328f6f8b418 3 months ago 3.97MB
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----
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Notice how large the application image `helloworld-jdk-9`.
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Run the `jdeps` tool to see what modules the application depends on:
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docker run -it --rm helloworld-jdk-9 jdeps --list-deps /opt/helloworld/helloworld-1.0-SNAPSHOT.jar
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and observe that the application only depends on the `java.base` module.
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=== Reduce the size of a Docker Image using JDK 9 and a Java application
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The Java application is extremely simple and as a result uses very little of the
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functionality shipped with JDK 9 distribution, specifically the application
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only depends on functionality present in the `java.base` module. We can create
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a custom Java runtime that only contains the `java.base` module and include
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that in application Docker image.
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Create a custom Java runtime that is small and only contains the `java.base`
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module:
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docker run --rm \
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--volume $PWD:/out \
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jdk-9-debian-slim \
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jlink --module-path /opt/jdk-9/jmods \
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--verbose \
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--add-modules java.base \
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--compress 2 \
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--no-header-files \
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--output /out/target/openjdk-9-base_linux-x64
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The JDK 9 tool `jlink` is used to create the custom Java runtime. The tool
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is executed from with the container containing JDK 9 and directory where the
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modules reside, `/opt/jdk-9/jmods`, is declared in the module path. Only the
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`java.base` module is selected.
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The custom runtime is output to the `target` directory:
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[source, text]
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----
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$ du -k target/openjdk-9-base_linux-x64/
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24 target/openjdk-9-base_linux-x64//bin
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12 target/openjdk-9-base_linux-x64//conf/security/policy/limited
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8 target/openjdk-9-base_linux-x64//conf/security/policy/unlimited
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24 target/openjdk-9-base_linux-x64//conf/security/policy
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68 target/openjdk-9-base_linux-x64//conf/security
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76 target/openjdk-9-base_linux-x64//conf
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44 target/openjdk-9-base_linux-x64//legal/java.base
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44 target/openjdk-9-base_linux-x64//legal
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72 target/openjdk-9-base_linux-x64//lib/jli
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16 target/openjdk-9-base_linux-x64//lib/security
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19824 target/openjdk-9-base_linux-x64//lib/server
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31656 target/openjdk-9-base_linux-x64//lib
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31804 target/openjdk-9-base_linux-x64/
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----
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To build Docker image for this application with the custom Java runtime create a
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new text file `helloworld-jdk-9-base.Dockerfile` with the following contents:
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[source, text]
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----
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# Hello world application with custom Java runtime with just the base module and Debian slim
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FROM debian:stable-slim
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COPY target/openjdk-9-base_linux-x64 /opt/jdk-9
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COPY target/helloworld-1.0-SNAPSHOT.jar /opt/helloworld/helloworld-1.0-SNAPSHOT.jar
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# Set up env variables
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ENV JAVA_HOME=/opt/jdk-9
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ENV PATH=$PATH:$JAVA_HOME/bin
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CMD java -XX:+UnlockExperimentalVMOptions -XX:+UseCGroupMemoryLimitForHeap \
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-cp /opt/helloworld/helloworld-1.0-SNAPSHOT.jar org.examples.java.App
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----
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Build a Docker image containing the simple Java application based of the Docker
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image `debian:stable-slim`:
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docker build -t helloworld-jdk-9-base -f helloworld-jdk-9-base.Dockerfile .
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List the images available using `docker image ls`:
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[source, text]
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----
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REPOSITORY TAG IMAGE ID CREATED SIZE
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helloworld-jdk-9-base latest 7052483fdb77 24 seconds ago 87.7MB
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helloworld-jdk9 latest eb0539e9529a 17 minutes ago 400MB
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jdk-9-debian-slim latest 023f6999d94a 5 hours ago 400MB
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jdk-9-alpine latest f5a57382f240 5 hours ago 356MB
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openjdk 9-jdk-slim 6dca67f4790e 3 days ago 372MB
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debian stable-slim d30525fb4ed2 4 days ago 55.3MB
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alpine 3.6 7328f6f8b418 3 months ago 3.97MB
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[source, text]
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----
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The `helloworld-jdk-9-base` is much smaller and could be reduced further if
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Alpine Linux was used instead of Debian Slim.
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A realistic application will depend on more JDK modules but it's still possible
|
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to significantly reduce the Java runtime to only the required modules (for
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example many applications will not require Corba or RMI nor the compiler tools).
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|
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@ -4,7 +4,9 @@ This tutorial offers Java developers an intro-level and self-paced hands-on work
|
|||
|
||||
* link:chapters/ch01-setup.adoc[Setup Environments]
|
||||
* link:chapters/ch02-basic-concepts.adoc[Docker Basic Concepts]
|
||||
* link:chapters/ch03-build-image.adoc[Build a Docker Image]
|
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* Building
|
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** link:chapters/ch03-build-image.adoc[Build a Docker Image]
|
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** link:chapters/ch03-build-image-java-9.adoc[Build a Docker Image for Java 9]
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* link:chapters/ch04-run-container.adoc[Run a Docker Container]
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* link:chapters/ch05-compose.adoc[Multi-container application using Docker Compose]
|
||||
* link:chapters/ch06-swarm.adoc[Multi-container application using Compose and Swarm Mode]
|
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|
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