Understanding Docker Image Size Concerns

What will you learn?

In this tutorial, we will delve into the common concern of large Docker image sizes. You will discover why your Docker images might be larger than expected and explore effective strategies to optimize and reduce their size without compromising functionality.

Introduction to Problem and Solution

When working with Docker, the efficiency in deployment it promises can sometimes be overshadowed by unexpectedly large image sizes. A 6.9GB Docker image may seem counterintuitive to the streamlined nature of containerization. The root causes often include the choice of base image, unnecessary layers, or including non-essential files within the image.

To tackle this issue, we will explore optimization techniques such as refining the Dockerfile, selecting more fitting base images, utilizing multi-stage builds efficiently, and being selective about what is included in the image. These practices can significantly diminish the size of Docker images while maintaining operational effectiveness.


# Use a smaller base image
FROM python:3.8-slim-buster as builder

# Install only necessary dependencies
RUN pip install --no-cache-dir flask gunicorn

# Multi-stage build: copy only necessary files from builder stage
FROM python:3.8-alpine
COPY --from=builder /usr/local/bin /usr/local/bin
COPY --from=builder /usr/local/lib/python3.8/site-packages /usr/local/lib/python3.8/site-packages

# Copy application code last (to leverage caching)
COPY . /app

CMD ["gunicorn", "-w 4", "myapp:app"]

# Copyright PHD


In this solution: – Choosing a Smaller Base Image: Initiating with python:3.8-slim-buster rather than heavier alternatives like python:3.8, significantly reduces the initial size. – No-Cache Installation: Using –no-cache-dir during pip installs avoids storing unnecessary files that won’t be utilized later. – Multi-Stage Builds: By transferring only essential content from one stage (builder) to another (alpine-based final stage), extraneous development tools or artifacts are prevented from bloating the final image. – Efficient Layering: Placing application code after setting up dependencies capitalizes on layer caching by Docker; modifications in app code won’t necessitate a complete rebuild of all layers.

These practices not only shrink overall size but also bolster security by limiting what’s included in the production image.

  1. How do I choose an appropriate base image?

  2. Look for official “slim” or “alpine” variants tailored for minimalism for your desired language/framework images.

  3. Can using .dockerignore help reduce my Docker image size?

  4. Absolutely! A well-crafted .dockerignore file ensures unwanted files aren’t copied into your docker context or images needlessly.

  5. What are multi-stage builds?

  6. Multi-stage builds enable clean separation between build-time and runtime environments within one Dockerfile, aiding in keeping production images compact yet efficient.

  7. Why should I avoid installing unnecessary packages?

  8. Additional packages introduce unused functionality leading to increased disk space usage and potential security vulnerabilities.

  9. Does ordering commands in my Dockerfile matter?

  10. Definitely! Command order influences caching; place stable commands before volatile ones for efficient re-builds.


Understanding factors contributing to large Docker images paves the way for more efficient container deployments. By meticulously selecting base images, leveraging multi-stage builds effectively, managing additions via .dockerignore, and optimizing Dockerfile practices like strategic command ordering – substantial reductions in docker file sizes can be achieved, enhancing operational efficiency across deployments.

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