The objective of this hands-on is to familiarize you with Docker.

Pulling and running an existing image

Pull a public image such as ubuntu or centos using the docker pull command. If a tag is not specified, docker will default to "latest".

$ docker pull ubuntu:14.04

Now run the image using the docker run command. Use the "-it" option to get an interactive terminal during the run.

$ docker run -it ubuntu:14.04
$ whoami
$ lsb_release -a

Making changes and committing them

Using standard linux commands, modify the image.

$ docker run -it ubuntu:14.04
root@949eb1a6a099:/# (echo '#!/bin/bash'|echo "echo 'Hello World'") > /bin/hello
$ chmod 755 /bin/hello
# Test it
$ hello
# Exit
$ exit

Now find the container and commit the changes to a new image called hello.

docker ps -a|head -2
# Grab the Container ID
docker commit <ID> hello

Now try running the new image with your changes.

docker run -it hello

Creating and Building a Dockerfile

While manually modifying and commiting changes is one way to build images, using a Dockerfile provides a way to build images so that others can understand how the image was constructed and make modifications.

A Dockerfile has many options. We will focus on a few basic ones (FROM, MAINTAINER, ADD, and RUN)

Create a simple shell script called script in your local directory using your favorite editor.

echo "Just say Hello World!"

Now create a file called Dockerfile in the same directory with contents similar to this. Use your own name and e-mail for the maintainer.

FROM ubuntu:14.04

ADD . /src
RUN cp /src/script /bin/hello && chmod 755 /bin/hello

Now build the image using the docker build command. Be sure to use the -t option to tag it. Tell the Dockerfile to build using the current directory by specifying .. Alternatively you could place the Dockerfile and script in an alternate location and specify that directory in the docker build command.

docker build -t hello:1.0 .

Try running the image.

docker run -it hello:1.0

Pushing a Dockerfile to dockerhub

Docker provides a public hub that can be use to store and share images. Before pushing an image, you will need to create an account at Dockerhub. Go to to create the account. Once the account is created, push your test image using the docker push command. In this example, we will assume the username is patsmith.

docker tag hello:1.0 patsmith/hello:1.0
docker push patsmith/hello:1.0

The first push make take some time depending on your network connection and the size of the image.

Docker architecture overview

Docker architecture