3.0 KiB
Undocker
Converts a Docker image (a bunch of layers) to a flattened "rootfs" tarball.
Project Status
The original author no longer uses Docker ecosystem, thus the project is abandoned. If you decide to fork and continue using it, ping me, I will link it to your fork from here.
Why?
Docker images became a popular way to distribute applications with their dependencies; however, Docker is not the best runtime environment. At least not for everyone. May boring technology run our software.
Undocker bridges the gap between application images (in docker image format) and application isolation ("container") runtimes: once the docker image is extracted, it can be run with old-fashioned tools: lxc, systemd-nspawn, systemd, FreeBSD Jails, and many others.
Installation
Build it like this for the "current" platform:
$ make undocker
make -B will print the extra flags (-X <...>) for cross-compiling with
other archs. It's all go build <...> in the back, and depends only on Go's
compiler and stdlib.
Usage: convert docker image to rootfs
Download busybox docker image from docker hub and convert it to a rootfs:
$ skopeo copy docker://docker.io/busybox:latest docker-archive:busybox.tar
$ undocker busybox.tar - | tar -xv | sponge | head -10; echo '<...>'
bin/
bin/[
bin/[[
bin/acpid
bin/add-shell
bin/addgroup
bin/adduser
bin/adjtimex
bin/ar
bin/arch
<...>
Refer here for other ways to download Docker images. There are many.
On author's laptop converting a 1.1GB Docker image with 77 layers takes around 3 seconds and uses ~65MB of residential memory.
Usage example: systemd
systemd-run \
--wait --pty --collect --service-type=exec \
-p RootDirectory=$PWD \
-p ProtectProc=invisible \
-p PrivateUsers=true \
-p DynamicUser=yes \
-- busybox httpd -vfp 8080
Systemd protections like PrivateUsers, DynamicUser, ProtectProc and
others are available, just like to any systemd unit.
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Contributions
The following contributions may be accepted:
- Patchsets, with accompanying tests.
- Regression reports.
If you found a container that undocker cannot extract, or extracts incorrectly and you need this that work with undocker, do not submit an issue: submit a patchset.
Reports of regression reports must provide examples of "works before" and "does not work after". Issues without an accompanying patch will most likely be rejected.
Communication
Feel free to ping me directly.
LICENSE
MIT