Choosing the Right Docker Base Image for Python Applications

In the early days of Python development, virtualenvwrapper was used for package isolation, but with Python 3 the built‑in venv became the standard. As application complexity grew, Docker emerged as an essential tool, prompting the need to choose an appropriate Docker base image for Python projects.

The article outlines the requirements for a Docker base image: stability across builds, timely security updates, up‑to‑date dependencies (e.g., GCC, OpenSSL), a rich library ecosystem, the latest Python version, a small image size, and long‑term support (LTS).

Four categories of base images are examined:

Traditional Linux distributions : Ubuntu 18.04 (LTS until 2023), CentOS 8 (updates until 2024, maintenance until 2029), Debian 10 (support until 2024).

Official Docker Python images : multiple Python versions, with variants based on Alpine, Debian Buster, and Debian Buster‑slim.

Amazon Linux 2 : AWS‑provided LTS image optimized for security and performance.

Alpine Linux : Minimalist distribution using musl instead of glibc , resulting in very small image sizes.

A size comparison (pull size) is presented in the table below:

Linux Distribution

Image Name

Pull Command

Size

Ubuntu

ubuntu:18.04

docker pull ubuntu:18.04

64.2MB

Alpine

alpine:latest

docker pull alpine:latest

5.59MB

Debian

debian:buster

docker pull amd64/debian:buster

114MB

CentOS

centos:8

docker pull centos:8

237MB

Amazon Linux 2

amazonlinux:latest

docker pull amazonlinux:latest

163MB

Debian

python:3.7

docker pull python:3.7

919MB

Alpine

python:3.7-slim

docker pull python:3.7-slim

179MB

Build‑time tests were performed using a simple Flask Dockerfile. The Dockerfile content is shown below:

<code># Dockerfile-flask
# Simply inherit the Python 3 image.
FROM python:3

# Set an environment variable
ENV APP /app

# Create the directory
RUN mkdir $APP
WORKDIR $APP

# Expose the port uWSGI will listen on
EXPOSE 5000

# Copy the requirements file in order to install Python dependencies
COPY requirements.txt .

# Install Python dependencies
RUN pip install -r requirements.txt

# Copy the rest of the codebase into the image
COPY . .

# Finally, we run uWSGI with the ini file
</code>

Build times for various base images were measured:

ubuntu:18.04 : 1 min 31.044 s

amazonlinux:latest : 30.898 s

debian:buster : 52.237 s

python:3.7 : 35.752 s

python:3.7‑slim : 53.475 s

alpine:latest : 24 min 43.122 s (significantly slower due to additional build tools and source compilation)

The extreme build time for Alpine is caused by the need to compile packages like matplotlib and pandas from source because Alpine uses musl instead of glibc , making pre‑compiled wheels incompatible.

Conclusions drawn:

Alpine is unsuitable as a base image for most Python applications due to missing glibc‑based binary wheels, despite its tiny size.

Amazon Linux 2 offers a balanced mix of stability, security, and performance for Python containers in AWS environments.

Ubuntu 18.04 and Debian 10 (Buster) are solid, middle‑ground choices; Debian is slightly newer.

The official Docker Python images provide no clear advantage and raise maintenance concerns.

Consistency of Linux distribution across a large fleet is important to avoid unforeseen risks.