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Motiejus Jakštys 2021-05-24 00:11:58 +03:00
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@ -6,13 +6,13 @@ Converts a Docker image (a bunch of layers) to a flattened "rootfs" tarball.
Why? Why?
---- ----
Docker images seems to be the lingua franca of distributing application Docker images became a popular way to distribute applications with their
containers. These are very wide-spread. However, is Docker the best runtime dependencies. However, Docker itself is not the best runtime environment. At
environment? Not for everyone. least not for everyone.
Undocker bridges the gap between application images (in docker image format) Undocker bridges the gap between application images (in docker image format)
and container runtimes: now you can run a Docker image with systemd-nspawn and container runtimes: now you can run a Docker image with old-fashioned
and/or lxc, without doing the `docker pull; docker start; docker export` dance. tools: lxc, systemd-nspawn or systemd itself.
Usage -- extract docker image Usage -- extract docker image
----------------------------- -----------------------------
@ -20,55 +20,49 @@ Usage -- extract docker image
Download `nginx` docker image from docker hub and convert it to a rootfs: Download `nginx` docker image from docker hub and convert it to a rootfs:
``` ```
skopeo copy docker://docker.io/nginx:latest docker-archive:nginx.tar skopeo copy docker://docker.io/busybox:latest docker-archive:busybox.tar
undocker rootfs nginx.tar - | tar -xv undocker rootfs busybox.tar - | tar -xv
``` ```
(the same can be done with `docker pull` and `docker save`) Almost the same can be done with a combination of `docker pull` and `docker
save`.
Usage -- systemd-nspawn example Usage -- systemd-nspawn example
------------------------------- -------------------------------
Once the image is converted to a root file-system, it can be started using Start with systemd-nspawn:
classic utilities which expect a rootfs:
``` ```
systemd-nspawn -D $PWD nginx -g 'daemon off;' systemd-nspawn -D $PWD busybox httpd -vfp 8080
``` ```
Usage -- lxc example Usage -- plain old systemd
-------------------- --------------------------
Preparing the image for use with lxc:
``` ```
undocker rootfs nginx.tar - | xz -T0 > nginx.tar.xz systemd-run \
undocker lxcconfig nginx.tar config --wait --pty --collect --service-type=exec \
tar -cJf meta.tar.xz config -p PrivateUsers=true \
-p DynamicUser=yes \
-p ProtectProc=invisible \
-p RootDirectory=$PWD \
-- busybox httpd -vfp 8080
``` ```
Import it to lxc and run it: Good things like `PrivateUsers`, `DynamicUser`, `ProtectProc` and other
[systemd protections][1] are available, just like to any systemd unit.
``` Notes & gotchas
lxc-create -n bb -t local -- -m meta.tar.xz -f nginx.tar.xz ---------------
lxc-start -F -n bb -s lxc.net.0.type=none
lxc-start -F -n bb -s lxc.net.0.type=none -- /docker-entrypoint.sh nginx -g "daemon off;"
```
Note: automatic entrypoint does not work well with parameters with spaces; not `unocker` does not magically enable you to run containers from the internet. In
sure what lxc expects here to make it work. fact, many will need significant tuning or not work at all. Thus you will still
need to understand what are you running.
About the implementation
------------------------
Extracting docker image layers may be harder than you have thought. See
`rootfs/doc.go` for more details.
The rootfs code is dependency-free (it uses Go's stdlib alone). The existing
project dependencies are convenience-only.
Contributions Contributions
------------- -------------
I will accept pull request for code (including tests) and documentation. I am I will accept pull request for code (including tests) and documentation. I am
unlikely to react to bug reports without a patch. unlikely to react to issue reports without a patch.
[1]: https://www.freedesktop.org/software/systemd/man/systemd.exec.html