efrecon/exodus

Exodus

This project is both an image and a proof-of-concept to build extremely minimal Docker images, but on top of the whole Debian catalog! Building uses https://github.com/intoli/exodus to create self-contained ***aries with their entire library dependencies and Docker https://docs.docker.com/develop/develop-images/multistage-build/ builds to squash away the original Debian context and installation. This results in images that contain the bare minimal to run the ***ary at hand. For example, packaging the jq ***ary takes 3.18MB instead of 80.3MB (on top of Debian Jessie) or 5.32MB (on top of Alpine, but this isn't a fair comparison).

How-To

The steps to create such minimal images are as follows:

1. Inherit from efrecon/exodus, this image is based on the latest https://hub.docker.com/_/python/ image, itself based on top of Debian https://hub.docker.com/_/debian/.
2. Add all the necessary software using regular apt-get update and apt-get install calls.
3. Use exodus to relocate the ***aries to temporary tarballs.
4. Untar the tarballs into some available locations, e.g. the HOME directory for the root user or similar.
5. Restart a new build from the e***y https://hub.docker.com/_/scratch/ image.
6. Copy back the ***aries from the HOME directory directly into / (this is safe, the image will not contain anything else).

Example

The following exemplifies these steps on https://stedolan.github.io/jq/.

Dockerfile
FROM efrecon/exodus

# Install whatever needed from debian
RUN apt-get update && \
    apt-get install -y jq

# Relocate the necessary binaries, and only those
RUN exodus --tarball jq --output /tmp/jq.tgz && \
    tar --strip 1 -C /root -zxvf /tmp/jq.tgz

# Restart from an empty image
FROM scratch

# Copy back the binaries, and maybe any configuration data or similar from the
# previous stage.
COPY --from=0 /root /

# You now have a minimal image!
ENTRYPOINT ["/bin/jq"]

Build this image using a command similar to:

Shell
docker build -t efrecon/jq .

On my system, the resulting image is 3.18MB, nothing more, nothing less...

Size Matters

Debian

By comparison, a similar image based on the following Dockerfile is 80.3MB.

Dockerfile
FROM debian:jessie-slim

RUN apt-get update && \
    apt-get install -y jq && \
    rm -rf /var/lib/apt/lists/*

ENTRYPOINT ["jq"]

Alpine

Building on top of Alpine with the following Dockerfile leads to a 5.32MB image instead. However, Alpine is built on top of the https://www.musl-libc.org/ library and has a smaller set of software packages available. https://github.com/intoli/exodus uses https://www.musl-libc.org/ to properly relocate the ***aries, but these will still depend of libc.

Dockerfile
FROM alpine

RUN apk --no-cache add jq

ENTRYPOINT ["jq"]

Acknowledgements

Nothing would be possible without https://github.com/intoli/exodus and its ability to relocate ***aries and their library dependencies.