Developer Cuts Docker Image 87% From 442 MB to 56 MB With Simple Optimizations

A software developer reduced a Python Flask microservice's Docker image size from 442 MB to 56.6 MB — an 87% reduction — by systematically redesigning its Dockerfile. The key changes included switching from the full python:3.12 base image to the leaner python:3.12-slim variant, removing unnecessary packages like curl, git, and vim that have no place in a production container. Additional improvements involved consolidating RUN instructions to avoid redundant image layers, reordering COPY commands to preserve Docker's layer caching, and adding a .dockerignore file to exclude test files and local environments. The hardened image also runs under a non-root system user instead of root, and replaces Flask's built-in development server with the production-grade Gunicorn WSGI server. The author notes that Debian slim was chosen over Alpine Linux due to better compatibility with Python packages that rely on C extensions.