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 exodus to create self-contained binaries with their entire library dependencies and Docker multi-stage builds to squash away the original Debian context and installation. This results in images that contain the bare minimal to run the binary at hand. For example, packaging the jq binary 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 python image, itself based on top of Debian jessie.
2. Add all the necessary software using regular apt-get update and apt-get install calls.
3. Use exodus to relocate the binaries 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 empty scratch image.
6. Copy back the binaries from the HOME directory directly into / (this is safe, the image will not contain anything else).

Example

The following exemplifies these steps on jq.

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:

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.

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 musl library and has a smaller set of software packages available. exodus uses musl to properly relocate the binaries, but these will still depend of libc.

FROM alpine

RUN apk --no-cache add jq

ENTRYPOINT ["jq"]

Acknowledgements

Nothing would be possible without exodus and its ability to relocate binaries and their library dependencies.