Dockerfile

# Dockerfile — packages the Flask app into a small Linux image for deployment.
#
# Why multi-stage is skipped here: for teaching, a single stage is easier to read.
# The app listens on port 5000 inside the container; docker-compose maps it to the host.

FROM python:3.12-slim-bookworm

# Safer Python behavior in containers
ENV PYTHONDONTWRITEBYTECODE=1
ENV PYTHONUNBUFFERED=1

WORKDIR /app

# Install dependencies first (better layer caching when only code changes)
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

# Application source
COPY . .

# Flask dev server — for real production, use gunicorn/waitress behind a reverse proxy
EXPOSE 5000

# Default command; docker-compose can override environment variables
CMD ["python", "app.py"]