How I Cut Docker Image Build Time from 16 Minutes to 1 Minute – 10× Faster Builds

Overview

The author describes a Python application whose Docker image originally required about 16 minutes to build and produced an ~8 GB image. By analysing the Dockerfile and applying a series of optimisations, the build time was reduced to roughly 1 minute and the image size to ~5 GB, achieving about a ten‑fold efficiency gain.

Initial Build Situation

The original Dockerfile (excerpt) and results are shown below:

FROM reg.docker.alibaba-inc.com/aci-images/python-service:3.8.0-63928922
# init folder
RUN mkdir -p /home/admin/logs && mkdir -p /home/admin/bin && mkdir -p /home/admin/conf && mkdir -p /home/admin/nginx && mkdir -p /home/admin/.maxhub/env_helper_util/zeta-local-env
# install zeta
RUN pushd /home/admin/.maxhub/env_helper_util/zeta-local-env && \
    wget https://artifacts.antgroup-inc.cn/artifact/repositories/softwares-common/antcode/zeta/0.7.9/zeta-linux-amd64-0.7.9.sh -O zeta-release.sh && \
    chmod +x zeta-release.sh && \
    ./zeta-release.sh --prefix=/usr/local && \
    popd
COPY --chown=admin:admin aml_core /home/admin/release/aml_core
COPY --chown=admin:admin backend /home/admin/release/backend
COPY --chown=admin:admin requirements.txt /home/admin/release/
RUN python3.10 -m venv /home/admin/run && \
    . /home/admin/run/bin/activate && \
    python3.10 -m pip install -i https://pypi.antfin-inc.com/simple-remote --upgrade pip && \
    python3.10 -m pip install -i https://pypi.antfin-inc.com/simple -r /home/admin/release/requirements.txt

Build time: ~16 minutes; Image size: ~8 GB.

Post‑Optimization Build

The optimised Dockerfile adopts a multi‑stage approach, moves rarely‑changed layers to the top, adds --no-cache-dir to pip install, removes unnecessary RUN chown commands, merges several RUN statements, and copies only the required artefacts from the builder stage.

# Stage 1: download dependencies
FROM reg.docker.alibaba-inc.com/antfin-sqa/amlregservermodel-dev:20241016125401_b0296dab as builder
COPY --chown=admin:admin requirements.txt /home/admin/release/
RUN python3.10 -m venv /home/admin/run && \
    . /home/admin/run/bin/activate && \
    python3.10 -m pip install -i https://pypi.antfin-inc.com/simple-remote --upgrade pip && \
    python3.10 -m pip install -i https://pypi.antfin-inc.com/simple -r /home/admin/release/requirements.txt --no-cache-dir

# Stage 2: final image
FROM reg.docker.alibaba-inc.com/aci-images/python-service:3.8.0-63928922
RUN mkdir -p /home/admin/logs /home/admin/bin /home/admin/conf /home/admin/nginx /home/admin/.maxhub/env_helper_util/zeta-local-env
COPY --chown=admin:admin conf/docker/build.yaml /root/
COPY --chown=admin:admin conf/docker/scripts/admin /home/admin
COPY --chown=admin:admin conf/nginx /home/admin/nginx
COPY --chown=admin:admin aml_core /home/admin/release/aml_core
COPY --chown=admin:admin backend /home/admin/release/backend
RUN chmod a+xw /home/admin/bin/fetch_ollama.sh /tmp

Result after optimisation: build time ~1 minute, image size ~5 GB.

Analysis Process

The longest‑running step was the

COPY --chown=admin:admin conf/docker/scripts/admin /home/admin

instruction, whose preceding step (downloading dependencies) consumed about 10 minutes. The base image itself was large (2.33 GB) and the pip cache added roughly 3.1 GB (2.6 GB dependencies + 729 MB cache). docker history was used to pinpoint the heavy layers.

Cache Invalidation Rules

Docker checks each instruction against cached layers; any change invalidates that layer and all subsequent layers.

ADD and COPY compute a checksum of file metadata; changes in file content invalidate the cache.

RUN instructions are cached based solely on the command string, not on the state of the container.

To force cache busting, you can modify a build‑arg, use docker builder prune, or build with --no-cache / --no-cache-filter.

Optimization Steps

Apply the static‑dynamic separation principle: place rarely‑changed commands (base image, dependency installation) early to maximise cache reuse.

Use multi‑stage builds to keep only the final artefacts in the runtime image.

Add --no-cache-dir to pip install to avoid large pip caches.

Remove or consolidate RUN chown commands, as each creates a new layer.

Merge consecutive RUN commands to reduce the total number of layers.

Select a smaller base image when possible (e.g., Alpine or a minimal Alibaba image).

Final Summary

Through systematic analysis and the above optimisations, the Docker image build time dropped from 16 minutes to about 1 minute and the image size was halved. The article also provides a checklist of Dockerfile best‑practice rules (limit to 20 instructions, avoid more than three consecutive RUN commands, place CMD/ENTRYPOINT after COPY/RUN, etc.) and a collection of additional tips such as using a .dockerignore file, running a single application per container, avoiding the latest tag, and adding health checks.