Docker images

• Use a common base image
• Stick to a fixed, known, stable version tag

Distinct 3 types of layers :

• Store layers (COPY, ADD) which increase image size (although not much)
• Compute/Build layers (RUN) which requires build time, and MIGHT impact on size if they generate artifacts.
• Metainformation layers (LABEL, ENTRYPOINT, EXPOSE, …) don't affect image size nor build time.

• If the commands imply artifact generation (downloads, builds), ensure to cleanup on the same layer to reduce size
• Put the most static (non-changing) layers first (building, files)
• Put the most dynamic (changing) layers last (metainformation)
• Metadata at the end (no-buildtime, no size)
• If you have common pre-setups put them first on distinct layers, so the layers can be shared across multiple images (and increase cache hit). You can also benefit from multistage builds.
• If there are many files, put them in a FS folder and copy them in one layer
• Remember you can use .dockerignore to reduce the context

• Start from zero version if still not released yet
• While developing always push images as :devel on registry
• If needed increase only release, then decide if major/minor increase is required (and restart release number)

• Ensure everything is commited and pushed
• Update dockerfile LABEL version
• Build and push with version-tag
• Final test
• Push same image with :stable (retag & push)
• Merge if needed
• git version over master and push tag

No hints here, just good shell script programming skills. Just a few guidelines focused on docker:

• Set safe defaults for ENV variables
• Test the script with stadnard shell (sh)
• Output to stdout and stderr
• Launch the main process with exec

FROM alpine:FIXED_VERSION

RUN true \
    && apk update \
    && apk add --no-cache \
        package \
        ... \
    && rm -rf /var/cache/apk/* \
    && true

# Copy start script
COPY *.sh /

EXPOSE 0000/tcp

ENTRYPOINT /entrypoint.sh

# Labels
LABEL name="lady/IMAGENAME"
LABEL summary="Description"
LABEL maintainer="Count Zero <count.zero@l3jane.net>"
LABEL version="0.0"
LABEL release="0"
LABEL vendor="Lady 3Jane"

• http://docs.projectatomic.io/container-best-practices/
• https://pythonspeed.com/articles/docker-caching-model/
• https://www.cloudbees.com/blog/best-practices-when-versioning-a-release/
• https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#add-or-copy