Dockerize your Python Application
Dockerfiles enable you to create your own images. A Dockerfile describes the software that makes up an image. Dockerfiles contain a set of instructions that specify what environment to use and which commands to run.
Creating a Dockerfile
First, start with a fresh empty directory. This directory defines the context of the build, meaning it contains all of the things needed to build my image.
Create a new text file in my_new_docker_build called Dockerfile (note no extension; on Windows, you may need to save the file as “All types” and put the filename in quotes to avoid automatically appending an extension). I am using the basic Python 3 image as my launching point. Add the following line to your Dockerfile:
FROM python:3
I want to run a basic Python script called my_script.py. First, add the script to the Dockerfile:
ADD my_script.py /
Our script depends on the Python pyStrich library (pyStrich generates 1D and 2D barcodes), so we need to make sure we install that before we run my_script.py!
Add this line to your Dockerfile to install random:
RUN pip install pystrich
Add this line to your Dockerfile to execute the script:
CMD [ "python", "./my_script.py" ]
Your Dockerfile should look like this:
FROM python:3
ADD my_script.py /
RUN pip install pystrich
CMD [ "python", "./my_script.py" ]
FROM tells Docker which image you base your image on (in the example, Python 3).
RUN tells Docker which additional commands to execute.
CMD tells Docker to execute the command when the image loads.
The Python script my_script.py looks like the following:
# Sample taken from pyStrich GitHub repository
# https://github.com/mmulqueen/pyStrich
from pystrich.datamatrix import DataMatrixEncoder
encoder = DataMatrixEncoder('This is a DataMatrix.')
encoder.save('./datamatrix_test.png')
print(encoder.get_ascii())
Run:docker build -t python-barcode
Run Your Image
After your image has been built successfully, you can run it as a container.
In your terminal, run the command docker images to view your images. You should see an entry for “python-barcode”. Run the new image by entering:
docker run python-barcode
You should see what looks like a large ASCII QR code.
Alternatives
If you only need to run a simple script (with a single file), you can avoid writing a complete Dockerfile. In the examples below, assume you store my_script.py in /usr/src/widget_app/, and you want to name the container my-first-python-script:
Python 3:
docker run -it --rm --name my-first-python-script -v "$PWD":/usr/src/widget_app python:3 python my_script.py
Python 2:
docker run -it --rm --name my-first-python-script -v "$PWD":/usr/src/widget_app python:2 python my_script.py
Further information
Creating a Dockerfile
Make sure you do not append an extension to the Dockerfile (i.e., Docker does not recognize Dockerfile.txt).You do not have to read the contents of every Dockerfile you base yours on, but make sure to at least familiarize yourself with them; you can avoid trying to install redundant software (e.g., installing pip when the Python image already loads it), and you can make sure you write your RUN commands appropriately. Docker Hub does not enforce basing all images off only one distribution of Linux; if you use a Debian-based distribution (Debian, Ubuntu, Mint, etc.) you need to call apt-get to install software, and if you use a Red Hat-based distribution (Red Hat Enterprise Linux/RHEL, CentOS) you need to use yum.
Gaining familiarity early prevents redoing your work and saves time.
You might end up starting with an unfamiliar base image (i.e., if you primarily use CentOS and want to run a Python installation, the Python image extends Debian Jessie, so you need to use caution in how you write your RUN directives). If you maintain familiarity with Ubuntu, using Debian does not offer too many challenges (Ubuntu came from an offshoot of Debian Linux).
Avoid putting any unused files in your build directory. Docker makes tarballs of everything in the current directory and sends that to the Docker daemon, so if you have unnecessary files, those are included.
Alternatives
Do not attempt to run a script requiring dependencies using the Alternative method, unless those dependencies come with the bare Python installation.
Deleting Docker Containers
Run the following command from your docker console to see a list of your containers:
docker ps
or
docker ps -a # to see all containers, including those not running
Note: Removing a Container is FINAL.
Delete a Single Container
Run docker ps -a and retrieve the container ID (an alphanumeric string, something like a39c259df462).
Run docker rm a39c259df462 to remove just that container.
Delete All Your Containers
To delete all your containers, run:
$ docker ps -q -a | xargs docker rm
-q prints only the container ID’s-a prints all containers passing all container IDs to xargs, docker rm deletes all containers
Deleting Docker Images
Delete a Single Image
Retrieve the Image ID using docker images (The Image IDs should be in the third column.)
Run docker rmi
$ docker rmi 60959f29de3a
Delete All Untagged Images
This requires a little bit of Linux magic (like deleting all containers above). Docker marks images without tags with “
docker rmi $(docker images | grep "<none>" | awk '{print $3}')
Delete All Images
To delete all of your images, you can simplify the command above:
docker rmi $(docker images | awk '{print $3}')
Delete Docker Containers
Usage:CommandDeletesallAll containers${id}The container corresponding to the container ID you pass
Delete Docker Images
Usage:CommandDeletesallAll imagesuntaggedImages tagged with “” (untagged images)${id}The image corresponding to the Image ID you pass