In order to create an application for Kubernetes deployment, we need to first create the application on the Docker. This can be done in two ways −

• By downloading
• From Docker file

By Downloading

The existing image can be downloaded from Docker hub and can be stored on the local Docker registry.

In order to do that, run the Docker pull command.

$ docker pull --help
Usage: docker pull [OPTIONS] NAME[:TAG|@DIGEST]
Pull an image or a repository from the registry
   -a, --all-tags = false     Download all tagged images in the repository
   --help = false             Print usage

Following will be the output of the above code.

The above screenshot shows a set of images which are stored in our local Docker registry.

If we want to build a container from the image which consists of an application to test, we can do it using the Docker run command.

$ docker run –i –t unbunt /bin/bash

From Docker File

In order to create an application from the Docker file, we need to first create a Docker file.

Following is an example of Jenkins Docker file.

FROM ubuntu:14.04
MAINTAINER [email protected]
ENV REFRESHED_AT 2017-01-15
RUN apt-get update -qq && apt-get install -qqy curl
RUN curl https://get.docker.io/gpg | apt-key add -
RUN echo deb http://get.docker.io/ubuntu docker main > /etc/apt/↩
sources.list.d/docker.list
RUN apt-get update -qq && apt-get install -qqy iptables ca-↩
certificates lxc openjdk-6-jdk git-core lxc-docker
ENV JENKINS_HOME /opt/jenkins/data
ENV JENKINS_MIRROR http://mirrors.jenkins-ci.org
RUN mkdir -p $JENKINS_HOME/plugins
RUN curl -sf -o /opt/jenkins/jenkins.war -L $JENKINS_MIRROR/war-↩
stable/latest/jenkins.war
RUN for plugin in chucknorris greenballs scm-api git-client git ↩
ws-cleanup ;
do curl -sf -o $JENKINS_HOME/plugins/${plugin}.hpi 
-L $JENKINS_MIRROR/plugins/${plugin}/latest/${plugin}.hpi ↩
; done
ADD ./dockerjenkins.sh /usr/local/bin/dockerjenkins.sh
RUN chmod +x /usr/local/bin/dockerjenkins.sh
VOLUME /var/lib/docker
EXPOSE 8080
ENTRYPOINT [ "/usr/local/bin/dockerjenkins.sh" ]

Once the above file is created, save it with the name of Dockerfile and cd to the file path. Then, run the following command.

$ sudo docker build -t jamtur01/Jenkins .

Once the image is built, we can test if the image is working fine and can be converted to a container.

$ docker run –i –t jamtur01/Jenkins /bin/bash