Building docker containers

Overview

Teaching: 5 min
Exercises: 10 min

Questions

• How do I create my own containers?

Objectives

• Understand how to build a recipe for a docker container.

Creating docker containers

So, you want to build your own docker containers? Excellent. You may be able to distribute your simulation or analysis code to others more easily without the need to support a wide range of platforms.

Creating a docker container involves writing a Dockerfile recipe. For the simplest of examples, let’s look back at the lolcow we started with, on the GitHub repository that houses the Dockerfile

FROM ubuntu:16.04

RUN apt-get update && apt-get install -y fortune cowsay lolcat

ENV PATH /usr/games:${PATH}
ENV LC_ALL=C

ENTRYPOINT fortune | cowsay | lolcat

The container uses Ubuntu 16.04 as a base layer, installs fortune, cowsay, and lolcat, sets the command search path, and defines an entry point (which is called when we run the container).

There is nothing more to writing a Dockerfile recipe than writing a shell script that specifies the steps to take to create container.

Storing a Dockerfile on GitHub allows integration with Docker Hub

The next step to creating your container on Docker Hub is greatly simplified by storing your Dockerfile on GitHub. This allows you to take advantage of automatic building on Docker Hub itself.

Build your own version of the lolcow container

Let’s recreate the lolcow container but instead use the most recent Ubuntu base layer, version 18.04.

1. Fork the lolcow GitHub repository to your personal GitHub account.
2. Modify the base layer FROM statement to reflect the newer Ubuntu version
3. Create an account on Docker Hub
4. Create an automated build based on GitHub.

Solution

It may take some time while Docker Hub creates your container, but you should end up with a GitHub repository like this one and a Docker Hub page like this one.

Depending on the order in which you complete the instructions, you may need to manually trigger your build on Docker Hub.

Key Points

• Although using containers with singularity does not require superuser privileges, creating containers still does.

• Dockerfiles are recipes for docker containers.

• By storing Dockerfiles in a GitHub repository we gain version both tracking and cloud building.