121 lines
3.1 KiB
Markdown
121 lines
3.1 KiB
Markdown
[](http://godocs.io/git.jakstys.lt/motiejus/undocker)
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Undocker
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--------
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Converts a Docker image (a bunch of layers) to a flattened "rootfs" tarball.
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Project Status
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--------------
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The project was announced to be deprecated in the beginning of 2024, but the
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maintainer has an interest in Docker ecosystem again, thus will maintain it
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somewhat starting at mid-2024.
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The author has some significant changes in mind, but the timeline is unknown.
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Why?
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----
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Docker images became a popular way to distribute applications with their
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dependencies; however, Docker is not the best runtime environment. At least not
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for everyone. May boring technology run our software.
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Undocker bridges the gap between application images (in docker image format)
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and application isolation ("container") runtimes: once the docker image is
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extracted, it can be run with old-fashioned tools: lxc, systemd-nspawn,
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systemd, FreeBSD Jails, and many others.
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Installation
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------------
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Build it like this for the "current" platform:
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```
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$ make undocker
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```
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`make -B` will print the extra flags (`-X <...>`) for cross-compiling with
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other archs. It's all `go build <...>` in the back, and depends only on Go's
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compiler and stdlib.
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Usage: convert docker image to rootfs
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-------------------------------------
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Download `busybox` docker image from docker hub and convert it to a rootfs:
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```
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$ skopeo copy docker://docker.io/busybox:latest docker-archive:busybox.tar
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$ undocker busybox.tar - | tar -xv | sponge | head -10; echo '<...>'
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bin/
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bin/[
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bin/[[
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bin/acpid
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bin/add-shell
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bin/addgroup
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bin/adduser
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bin/adjtimex
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bin/ar
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bin/arch
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<...>
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```
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Refer [here][2] for other ways to download Docker images. There are many.
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On author's laptop converting a [1.1GB Docker image with 77
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layers](https://hub.docker.com/r/homeassistant/home-assistant) takes around 3
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seconds and uses ~65MB of residential memory.
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Usage example: systemd
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----------------------
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```
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systemd-run \
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--wait --pty --collect --service-type=exec \
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-p RootDirectory=$PWD \
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-p ProtectProc=invisible \
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-p PrivateUsers=true \
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-p DynamicUser=yes \
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-- busybox httpd -vfp 8080
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```
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[Systemd protections][1] like `PrivateUsers`, `DynamicUser`, `ProtectProc` and
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others are available, just like to any systemd unit.
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Similar Projects
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----------------
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* [rootfs_builder](https://github.com/ForAllSecure/rootfs_builder)
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Contributions
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-------------
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The following contributions may be accepted:
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- Patchsets, with accompanying tests.
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- Regression reports.
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If you found a container that undocker cannot extract, or extracts incorrectly
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and you need this that work with undocker, do not submit an issue: submit a
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patchset.
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Reports of regression reports must provide examples of "works before" and "does
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not work after". Issues without an accompanying patch will most likely be
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rejected.
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Communication
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-------------
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Feel free to ping me [directly][motiejus-comms].
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LICENSE
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-------
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MIT
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[1]: https://www.freedesktop.org/software/systemd/man/systemd.exec.html
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[2]: https://fly.io/blog/docker-without-docker/
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[motiejus-comms]: https://jakstys.lt/contact/
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