Single-Stage or Multi-Stage Docker Builds

#docker

Understanding Docker Builds

While containerizing the School Management Flask API, I explored single-stage and multi-stage Docker builds to understand their impact on performance, image size, and deployment efficiency. This exploration taught me practical lessons about optimizing images, improving CI/CD pipelines, and separating build-time dependencies from runtime environments.

Single-Stage Builds

A single-stage build uses one image for both building and running the application. All dependencies, build tools, and source code are included in the final image.

Example:

FROM python:3.12-slim


WORKDIR /app


COPY requirements.txt .


RUN pip install --no-cache-dir -r requirements.txt


COPY . .


RUN chmod +x /app/entrypoint.sh


EXPOSE 5000


ENTRYPOINT ["/app/entrypoint.sh"]

Key Takeaways:

  • Simple and straightforward to set up
  • Includes all build and runtime dependencies in one image
  • Final image may be larger and include unnecessary build artifacts

My Experience:

  • Measured build time: ~1.67s
  • Image contained build tools and cached files, resulting in a larger final image

Multi-Stage Builds

A multi-stage build separates build-time dependencies from the runtime environment. You compile or build your app in a full-featured image, then copy only the necessary artifacts into a smaller, cleaner runtime image.

Example:

# Stage 1 - builder
FROM python:3.12-slim AS builder


WORKDIR /app


COPY requirements.txt /app/


RUN pip install --no-cache-dir -r requirements.txt




# Stage 2 - final image
FROM python:3.12-slim


WORKDIR /app


COPY --from=builder /usr/local/lib/python3.12/site-packages /usr/local/lib/python3.12/site-packages
COPY --from=builder /usr/local/bin /usr/local/bin


COPY . .


RUN chmod +x /app/entrypoint.sh


EXPOSE 5000


ENTRYPOINT ["/app/entrypoint.sh"]

Key Takeaways:

  • Separates build-time dependencies from the runtime image
  • Produces a smaller, cleaner final image
  • Improves maintainability and keeps runtime focused

My Experience:

  • Measured build time: ~1.08s (faster on my system)
  • Multi-stage image excluded build tools and cached files, resulting in a cleaner, focused image
  • Slightly more complex Dockerfile, but worth it for maintainability

Why It Matters

For small projects like the School Management API, build speed and image size differences may be minimal, and results depend on your system (CPU, RAM, disk speed). However, understanding these approaches still provides benefits for maintainability, security, and best practices.

  • Reduces unsed files in production images
  • Optimizes CI/CD pipelines and deployment efficiency
  • Encourages better project structure by separating build and runtime concerns

Key Learning

Exploring the differences between single-stage and multi-stage builds was a great opportunity to see how both approaches behave. Even for a small project like the School Management API, multi-stage builds produced smaller, cleaner images, while single-stage builds were simpler to set up. This exercise helped me better understand build optimization and containerization concepts for personal learning.

Thank you

Big thanks for reading! You’re awesome, and I hope this post helped. Until next time!