dockerize your app

I had time to play with Docker so I was able to create an example how to dockerize java application with minimal effort.

Let’s dockerize JAX-RS resource served on Grizzly container. This app is simple as it can be and it is essentially Jersey Hello World Example with some small changes. My only contribution is Dockerfile template and a couple gradle tasks which make all distribution files you need to create a docker image.

configuration

There are only few configuration options centralized into build.gradle and dockerize gradle task which replaces tokens like BASE_IMAGE in build directory.

ext {
    // lib version
    jerseyVersion = "2.14"

    // dockerfile template attributes
    baseImage = "dockerfile/ubuntu"
    port = "4004"
}

task dockerize(type: Copy, dependsOn: tasks.fatJar) {
    from 'src/main/dist/Dockerfile'
    into "${buildDir}/dockerize"
    filter(ReplaceTokens, tokens: [APP_NAME   : project.name,
                                   APP_VERSION: project.version,
                                   BASE_IMAGE : baseImage,
                                   PORT       : port])
}

Tokens used by a template will be replaced with values defined in dockerize task.

#
# @APP_NAME@ dockerfile.
#

# Pull base image.
FROM @BASE_IMAGE@

# Install Java.
RUN \
  echo oracle-java8-installer shared/accepted-oracle-license-v1-1 select true | debconf-set-selections && \
  add-apt-repository -y ppa:webupd8team/java && \
  apt-get update && \
  apt-get install -y oracle-java8-installer && \
  rm -rf /var/lib/apt/lists/* && \
  rm -rf /var/cache/oracle-jdk8-installer

# Define commonly used JAVA_HOME variable
ENV JAVA_HOME /usr/lib/jvm/java-8-oracle

COPY ./@APP_NAME@-@APP_VERSION@.jar /@APP_NAME@/

# Define working directory.
WORKDIR /work-dir

ENTRYPOINT ["java", "-jar", "/@APP_NAME@/@APP_NAME@-@APP_VERSION@.jar"]

EXPOSE @PORT@

build app

Distribution task makes all resources you need and places them into ${buildDir}/distribution.

Dockerfile - transformed template located in src/main/dist
fat jar - contains all needed classes

gradle distribution

Distribution task depends on dockerize task and fatjar task.

build a docker image

Directory ${buildDir}/distribution contains all you need to create docker image. Go to the distribution directory and build a docker image with tag jersey\hello

cd build/distribution
docker build -t jersey/hello .

run docker image

Argument -p means publishing exposed port to the host. We configured Grizzly be running on port 4004 and we publish it as 4001 at host.

docker run -p 4001:4004 -d --name hello-4001 jersey/hello

Then check the container is running

docker ps

Output should look like this

CONTAINER ID        IMAGE                 COMMAND                CREATED             STATUS              PORTS                    NAMES
9656759a854d        jersey/hello:latest   "java -jar /dockeriz   10 minutes ago      Up 8 seconds        0.0.0.0:4001->4004/tcp   hello-4001

test

curl localhost:4001/base/helloworld

…and here we go

Hello World!

Repo on GitHub