Table of Contents

A Star Wars Docker Tutorial

Objectives

Upon completion of this session, you should understand how to:

1. Run and interact with docker image
2. Author a Dockerfile, build it, and run it
3. Identify at least one use case where containerization is useful

Context

You are working as a consultant for 1-900-STAR-WARZ, a paid call-in telephone service for researching Star Wars facts. This a niche service where the customer base consists of new and veteran Star Wars fanatics who are usually either:

1. boomers, who do not know how to internet
2. conspiracy theorist who do not want to internet

Effectively, they provide a VPN-by-telephone service.

Current Need

Provide a command line solution for looking up a Star Wars character and their homeworld.

Restrictions

1. Employees of 1-900-STAR-WARZ are allowed internet access but only from a linux terminal. They are not allowed to use web browsers or other GUI applications because they require too much RAM and mouse clicking.
2. Customer would like to be able to maintain this solution on their own.
   1. Is only familiar with shell scripting (no python or nodejs please)
   2. Prefers Ubuntu or other debian variant of linux
   3. Wants to minimize disk utilization
   4. Prefers httpie over curl
   5. Does not want to install any additional dependencies on employee computers other than Docker

Exercise

The following exercise requires a working container Docker installation. Podman will work just fine as well. It is also assumed you know your way around a linux-based terminal.

• Podman
• Docker Desktop

Run a Docker Image in a Container

How to find an appropriate docker image?

• dockerhub: https://hub.docker.com/
• Amazon ECR Public: https://gallery.ecr.aws/
• Microsoft Artifact Registry: https://mcr.microsoft.com/

To review:

• image publisher
• image size
• image contents
• security concerns

For this exercise, we’ll use debian:bullseye-slim

😎 PROTIP: You will learn more through muscle memory by typing the following commands and NOT copy/pasting.

Hello docker

Enter the following in a terminal:

docker run debian:bullseye-slim echo Hello docker

What just happened??

1. A docker image was downloaded from DockerHub (the default)
2. A container was started with this image as a container and executed the provided command of echo Hello docker

Try running the same command again. Does it take less time? Docker caches downloaded images

Now try the following caommands:

docker run -it --rm debian:bullseye-slim
echo Hello docker
exit

What just happened??

1. We created and ran a docker image with an interactive terminal (-i and -t params)
2. Did you notice the change in shell prompt after line 1?
   • You are now in an isolated Linux container
   • The default command on the Docker file is bash. As a result, you get a bash terminal/shell. Reference.
3. exit closes the shell, which detaches from the container.
4. The docker run argument, --rm, automatically removes the container on exit and frees up that disk space
5. An image can be run as many container instances on the same system. --rm removes the container, not the image. Try the following command to confirm the image is still on your computer:

docker image ls

Experimenting with a Solution

We will use swapi.dev to perform the character lookup.

// example request
GET <https://swapi.dev/api/people/?search=luke>

// example response (truncated to relevant data)
{
    "count": 1,
    "next": null,
    "previous": null,
    "results": [
        {
            "name": "Luke Skywalker",
            "homeworld": "https://swapi.dev/api/planets/1/"
        }
    ]
}

Back to the Container!

Let’s see if we can request and parse only the relevant data in the container

# get a bash shell in a container

docker run -it --rm debian:bullseye-slim

# install httpie and jq

apt update && apt install httpie jq -y

# try the http request

# NOTE: `--print b` will ensure that only the response body is emitted

http --print b <https://swapi.dev/api/people/?search=luke>

# now, let's limit the output to what we need

http --print b <https://swapi.dev/api/people/?search=luke> | jq '.results[] | { name: .name, homeworld: .homeworld }'

Build a Docker file

Ideally, the customer should not have to run all of the above commands to perform a look up. And the customer does not want to install httpie and jq on all computers. Instead we can bundle the solution into our own docker image based on the debiean:bullseye-slim image. How do we simplify the solution to just the desired input and output?

To begin, create a directory for the solution and some files.

mkdir ~/star-warz
cd ~/star-warz
touch Dockerfile
touch run.sh

Define the Dockerfile: Iteration 1

Edit the files as follows

Dockerfile

# This is the base image for our image
FROM debian:bullseye-slim

# Install the required dependencies
# The arguments -y and --no-install-recommends will avoid any unecessary prompts
RUN apt update && apt install httpie jq -y --no-install-recommends

# Copy a script into the docker image, and make it executable
COPY run.sh .
RUN chmod +x run.sh

# Define the entrypoint for docker run
ENTRYPOINT [ "./run.sh" ]

run.sh

# !/bin/bash

http --print b <https://swapi.dev/api/people/?search=luke> | jq '.results[] | { name: .name, homeworld: .homeworld }'

How do we run it?

# build the image
# -t specifies a tag for the image, otherwise, the image is only identifiable by its hash
docker build . -t star-warz

# run it
# WARNING: here -t does not mean "tag", it is setting up a terminal
docker run --rm -t star-warz

What just happened?

1. We built a new docker image with a tag of star-warz. Try running docker image ls and confirming its existence
2. We ran the image with a terminal and exited.
3. We should have seen the search results for luke

How do we make it re-usable?

luke is hard-coded in run.sh To enable the solution to accept a search term from the command line requires a small change.

Edit run.sh as follows

# !/bin/bash

http --print b <https://swapi.dev/api/people/?search=$1> | jq '.results[] | { name: .name, homeworld: .homeworld }'

Build and run again

docker build . -t star-warz && docker run --rm -t star-warz

Run more searches

docker run --rm -t star-warz luke

docker run --rm -t star-warz anakin

Additional Exercises

1. Currently, the response for homeworld is a URL. The customer would like to see the homeworld name instead.
2. How could you further simplify the solution?