Python Docker Images in less than 50MB

I’m Python developer and Docker user. I like Python. It’s simple and developing process is very fast, but usually it’s not the best choice if you want a small distributable software.

It’t very common that a Python project is packaged as Docker Image with some hundreds of MB. Even for a small projects! But don’t worry. Here you have a trick to create smaller Docker Python images.

Oks, we want to package a project with this typical scaffolding:

$ ls -lh demo_app/
-rw-r--r--  1 Dani  staff     1B May 25 10:31 Dockerfile
-rw-r--r--  1 Dani  staff     2B May 25 09:28 MANIFEST.in
drwxr-xr-x  2 Dani  staff    64B May 25 09:27 app
-rw-r--r--  1 Dani  staff     9B May 25 09:27 requirements.txt
-rw-r--r--  1 Dani  staff     0B May 25 09:27 setup.py

The process will be as the following:

1. Write a multi-step Docker file.
2. Start with a Python base image.
3. Create a Python wheel building step with python optimization flags.
4. Create the final layer and install the built wheels avoiding using Pypi index server.

Then we create this Dockefile:

FROM python:3.8-alpine as base

RUN apk update && \
    apk upgrade

FROM base as builder

RUN apk add --no-cache build-base && \
    python -m pip install --no-cache-dir -U pip wheel

COPY ./ /app/
RUN python -OO -m pip wheel --no-cache-dir --wheel-dir=/root/wheels -r /app/requirements.txt && \
    python -OO -m pip wheel --no-cache-dir --wheel-dir=/root/wheels /app/

FROM base
COPY --from=builder /root/wheels /root/wheels

RUN python -m pip install --no-cache --no-index /root/wheels/*
RUN rm -rf /root/wheels

ENTRYPOINT ["my-project"]

We only must pay attention to two things:

Int the first one we were installed the project dependencies and our own project:

RUN python -OO -m pip wheel --no-cache-dir --wheel-dir=/root/wheels -r /app/requirements.txt && \
    python -OO -m pip wheel --no-cache-dir --wheel-dir=/root/wheels /app/

The second one we were installed only wheels we were created in the previous steps avoiding pip access to Pypi server for download anything:

RUN python -m pip install --no-cache --no-index /root/wheels/*

So the resulting Docker image will only contains binaries generated code by wheels without optimization Python flags