Creating Containers with Docker

Overview

Questions

• How do you create new Docker images?

Objectives

• Explain how a Dockerfile is used to create Docker images
• Create a Dockerfile to run a command
• Use docker build to create a new image
• Update a Dockerfile to run a Python script

Introduction

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TODO Dockerfiles -> Images -> Containers

TODO Might be a good spot for a visual.

TODO How do we extend analogies that we presented in episode 1?

Dockerfile gross anatomy

TODO Cover two commands: FROM and CMD (or maybe ENTRYPOINT instead of CMD?)

Creating images from Dockerfiles

TODO Explain commands. Note how no new file is created in our directory, it gets created…somewhere, though?

docker build -t ...

docker image ls

Starting containers

TODO This is review.

docker run ...

Confirm it ran and quit

docker ps -a

Challenge 1: Update base image

• Update the Dockerfile to have a base image that includes Python version 3.12 (instead of Python version 3.9)
• Build the image
• Start the container to confirm it is using Python version 3.12

Update the Dockerfile

To change the base image, update the information passed to the FROM command. That is, open the Dockerfile and change this line:

FROM python:3.9

to

FROM python:3.12

Buid the image

In the terminal, use docker build to create a new version of the image.

BASH

docker build -t <username>/python-container

This command will over-write the previous version of the image. TODO Need to test this statement.

Verify image was updated

In the terminal, use docker run to start a container based on the updated image.

BASH

docker run <username>/python-container

Copying files into the image

TODO Add flavor text about why we might do this.

COPY ...

See https://stackoverflow.com/questions/32727594/how-to-pass-arguments-to-shell-script-through-docker-run and https://www.tutorialspoint.com/how-to-pass-command-line-arguments-to-a-python-docker-container

for example of passing arguments to a script. Passing arguments might be too much.

Challenge 2: Copy a script to run in the container

There is a script (make this a print("Hello World!") python script) you want to include

Show me the solution

Key Points

• Dockerfiles include instructions for creating a Docker image
• The FROM command in a Dockerfile indicates the base image to build on
• The CMD command in a Dockerfile includes commands to execute when a container starts running
• The COPY command in a Dockerfile copies files from your local machine to the Docker image so they are available for use when the container is running