Creating a Docker Image with Ubuntu and Java

This short article shows how to create a Docker image with Ubuntu 15.04 and that has Java 7 or 8 installed. It will act as a base for some future articles that I have planned to write.

Yes, I am aware that there are several Docker images with Java 8 on Docker Hub.

Prerequisites

When writing this article, I have used Docker 1.7.1 and Docker-Machine 0.3.0. Instructions on how to install these can be found here.

Docker File

The Docker documentation recommends that Docker files are to be located in a dedicated directory which only contains the files necessary for the creation of the Docker image.

I have thus created a directory named “krizsan-ubuntu1504java8” for the Docker image with Java 8 and another directory named “krizsan-ubuntu1504java7” for the image with Java 7.
Each of these directories are to contain a file named “Dockerfile” (note: no file extension!).

The Docker file for Java 8 on Ubuntu 15.04 has the following contents:

# Ubuntu 15.04 with Java 8 installed.
# Build image with:  docker build -t krizsan/ubuntu1504java8:v1 .

FROM ubuntu:15.04
MAINTAINER Ivan Krizsan, https://github.com/krizsan
RUN apt-get update && \
    apt-get upgrade -y && \
    apt-get install -y  software-properties-common && \
    add-apt-repository ppa:webupd8team/java -y && \
    apt-get update && \
    echo oracle-java7-installer shared/accepted-oracle-license-v1-1 select true | /usr/bin/debconf-set-selections && \
    apt-get install -y oracle-java8-installer && \
    apt-get clean

The short version is that this Docker file will create a Docker image based on the ubuntu:15.04 Docker image in which Oracle’s Java 8 is installed.

Long version, row-by-row:

•  FROM ubuntu:15.04 
  States which Docker image this Docker image is to be based upon. Compare to parent class in object-oriented programming.
•  MAINTAINER Ivan Krizsan, https://github.com/krizsan 
  Tells us who is maintaining this Docker image.
• The Docker RUNcommand executes shell commands to install programs, configure the Docker image etc.
  Details follow below on the purpose of each shell command.
•  apt-get update 
  Updates the list of available packages and their versions.
•  apt-get upgrade 
  Installs any newer versions of currently installed packages.
•  apt-get install -y software-properties-common 
  Installs software in order to allow for independent vendor software sources, in particular the “add-apt-repository” command that is used in the next line.
•  add-apt-repository ppa:webupd8team/java -y 
  Adds the PPA repository that contains Oracle Java 8, assuming yes to all queries.
•  apt-get update 
  Again, updates the list of available packages and their versions. The reason for running an update again is that a new repository was just added and we want to refresh the list of available packages and their versions, including those in the new repository.
•  echo oracle-java7-installer shared/accepted-oracle-license-v1-1 select true | /usr/bin/debconf-set-selections 
  The Java installer require you to accept a license before the installation begins. This line automates accepting the license.
•  apt-get install -y oracle-java8-installer 
  Finally Java 8 can be installed! The -y flag runs the installation in a non-interactive mode, assuming that all questions are to be answered “yes.”
•  apt-get clean 
  Cleans the local repository from retrieved package files.

The reason for having one single Docker RUN  command and chaining the shell commands using &&   is that Docker will create one additional layer on the image for each RUN   command. The fewer RUN   commands that a Docker file contains, the smaller will the resulting image be.

The Docker file that will create an image with Java 7 on Ubuntu 15.04 looks like this:

# Ubuntu 15.04 with Java 7 installed.
# Build image with:  docker build -t krizsan/ubuntu1504java7:v1 .

FROM ubuntu:15.04
MAINTAINER Ivan Krizsan, https://github.com/krizsan
RUN apt-get update && \
    apt-get upgrade -y && \
    apt-get install -y  software-properties-common && \
    add-apt-repository ppa:webupd8team/java -y && \
    apt-get update && \
    echo oracle-java7-installer shared/accepted-oracle-license-v1-1 select true | /usr/bin/debconf-set-selections && \
    apt-get install -y oracle-java7-installer && \
    apt-get clean

The only difference compared to the Java 8 Docker file, apart from the comments, is the line second-to-last in which the Java 7 installer is used.

Build the Java 8 Docker image using the following steps:

• Open a terminal window.
• If you are not using a Linux operating system, create a Docker-Machine (if you don’t already have one):
   docker-machine create dev 
  
• If you are not using a Linux operating system, start the Docker-Machine:
   docker-machine start dev 
  
• If you are not using a Linux operating system, ssh into the Docker-Machine:
   docker-machine ssh dev 
  
• Go to the directory containing the Docker-file which describes the image you want to build.
  In this example, I will build the Java 8 image.
• Build the Docker image:
   docker build -t krizsan/ubuntu1504java8:v1  .
  Note the period at the end of the line!
  Linux users will need to add the sudo command before the Docker command:
   sudo docker build -t krizsan/ubuntu1504java8:v1  .
  You will see quite some console output that should end with something like this:

...
update-alternatives: using /usr/lib/jvm/java-8-oracle/bin/xjc to provide /usr/bin/xjc (xjc) in auto mode
Oracle JDK 8 installed
...
invoke-rc.d: policy-rc.d denied execution of start.
Setting up xfonts-encodings (1:1.0.4-2) ...
Setting up xfonts-utils (1:7.7+2) ...
Setting up gsfonts-x11 (0.22) ...
Processing triggers for libc-bin (2.21-0ubuntu4) ...
Processing triggers for systemd (219-7ubuntu6) ...
 ---> d3c43c2de29e
Removing intermediate container f447de6f01c6
Successfully built d3c43c2de29e

• Start a Docker container using the newly created Docker image:
   docker run -it krizsan/ubuntu1504java8:v1 bash 
  Again, Linux users need to insert the sudo command before the docker command.
• Verify the Java version installed:
   java -version 
  In my case I see that Java version 1.8.0_51 is installed.
• Exit the Docker container:
   exit 
  

Finally, while still being let’s examine the size of the image that was created:

REPOSITORY                TAG                 IMAGE ID            CREATED             VIRTUAL SIZE
krizsan/ubuntu1504java8   v1                  3f1e02768a70        16 seconds ago      802.6 MB

The size of the image is on the right, in the  VIRTUAL SIZE column, and, as you can see is around 803MB.

This concludes this article and I am now ready to create further Docker images containing software that runs on Java.