This page describes a very simple project with a ''Dockerfile'' and a ''Makefile'' as required for all projects and theses supervised in our group. The basic idea is really easy: if you were afraid of Docker before, you won't be anymore after reading this page.

<<TableOfContents(2)>>

= Example Project =

Let's consider a tiny example project, which consists of a single ''Makefile'' with the following contents (the first character in the second line must be TAB, this is standard Makefile syntax):

{{{
help:
        @echo "Help yourself before you help others :-)"
}}}

= Dockerfile =

In the same folder as your Makefile, create a file ''Dockerfile'' with the following contents:

{{{
FROM ubuntu:16.04
MAINTAINER Firstname Lastname <your@ma.il>
RUN apt-get update && apt-get install -y make vim
COPY Makefile Makefile
CMD ["/bin/bash"]

# docker build -t docker-example .
# docker run -it docker-example
}}}

The first line (FROM ...) says that we want to build an image based on Ubuntu 16.04. The second line (MAINTAINER ...) is purely informational, you should of course use your own name and email address here. The third line (RUN ...) installs make and vim in the image (it's a naked Ubuntu 16.04, with almost nothing pre-installed). The fourth line (COPY ...) copies the Makefile to the image (you can also copy whole directories here). The fifth line (CMD) specifies the command to be run when you run the container (in this case, we will be in an interactive bash shell).

= Building the image and running it in a container =

Now we can build the image (conceptually, a whole Ubuntu 16.04 with our Makefile from above in it, in reality, Docker will reuse as much as possible from the machine on which you are building the image) and run it inside a container:

{{{
docker build -t docker-example .
docker run -it docker-example
}}}

The -t option in the first line specifies a name and the . says that docker should look for everything in the current directory. The -it option in the second line says that we want to run in interactive mode.

After the commands above, you should see a prompt of the following kind

{{{
root@4b3dbcdd8fff:/#
}}}

The ''root'' says that you are the root user (but only inside of this container). The part after the @ is the name of the container. You can now do 'ls -l' and you will see the typical directory structure of Ubuntu, as well your ''Makefile''. You can edit it with ''vim'' if you like. Or you can just run ''make''. 
Note that we explicitly specified in the Dockerfile to install ''vim'' and ''make'', otherwise the two commands would not be available (but we could install them ourselves in the container with ''apt-get install ...'', but we would have to do that every time we run the container).

= Testing the Dockerfile on our machines =

On our machines you cannot run ''sudo docker'', because of security reasons. Instead, on ''tapoa'' and ''metropolis'', we have made available ''wharfer'', which can be used just like ''docker'', but without the security risks. So on those machines, you can run (with the same effect as described above):

{{{
wharfer build -t docker-example .
wharfer run -it docker-example
}}}