10 Proven Ways to Shrink Your Docker Image Size

Docker is a container engine that runs code in isolated environments, and Docker images package applications with all their dependencies. Large images increase attack surface, slow transfer, and prolong deployment, so optimizing image size is essential.

1. Minimize Image Layers

Each FROM, RUN, and COPY instruction creates a separate layer, inflating the image. Combine related commands into a single RUN or COPY to reduce layers.

RUN apt install unzip -y && \
    apt install python3 -y

Combining commands can save several megabytes, as shown in the accompanying diagram.

2. Use Docker‑Squash

Docker creates many layers during a build; squashing merges them into a more compact structure. pip install docker-squash Then run:

docker-squash image:old -t image:new

3. Choose Smaller Base Images

Switch from full images to slim or Alpine variants. For Python, python:3.9-slim (~1 GB) is much smaller than python:3.9 (~1.3 GB), and python:3.9-alpine is only about 49 MB.

4. Multi‑Stage Builds

Separate build and runtime stages, copying only the necessary artifacts to the final image.

# Official build image
FROM node:14.17-alpine3.14 as build

COPY public /home/app/public/
RUN apk add g++ make python2 && \
    apk --purge del python2

COPY nginx.conf /etc/nginx/conf.d/default.conf
COPY --from=build /home/app/build /usr/share/nginx/html
CMD ["nginx", "-g", "daemon off;"]

5. Use --no-install-recommends with apt

Prevent installation of unnecessary recommended packages.

apt install unzip -y --no-install-recommends && \
apt install curl -y --no-install-recommends && \
apt install python3 -y --no-install-recommends

6. Clean APT Cache After Installation

Remove the package list to free space.

apt install unzip -y --no-install-recommends && \
apt install curl -y --no-install-recommends && \
apt install python3 -y --no-install-recommends && \
rm -rf /var/lib/apt/lists/*

7. Use a .dockerignore File

Exclude unnecessary files (e.g., .git, docs) from the build context to keep the image lean.

8. Place COPY After RUN When Possible

Doing so improves cache reuse, reducing rebuild time and image size.

apt install unzip -y --no-install-recommends && \
apt install curl -y --no-install-recommends && \
apt install python3 -y --no-install-recommends && \
rm -rf /var/lib/apt/lists/*

9. Delete Installation Artifacts

Remove downloaded archives after installing packages, such as the AWS CLI zip file.

RUN curl "https://awscli.amazonaws.com/awscli-exe-linux-x86_64.zip" -o "awscliv2.zip" && \
    unzip awscliv2.zip -d /tmp && \
    ./aws/install && \
    rm -rf awscliv2.zip /tmp/aws

10. Use Image‑Sizing Tools

Tools like Dive , fromlatest.io , and Docker Slim analyze Dockerfiles and images to suggest further reductions.

https://github.com/wagoodman/dive

https://www.fromlatest.io/

https://github.com/slimtoolkit/slim

Applying these ten methods can dramatically shrink Docker images, improve security, and speed up deployments.