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undocker
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Motiejus Jakštys 2021-05-24 00:11:58 +03:00
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Undocker
--------
Convert a Docker image to a root file system.
Converts a Docker image (a bunch of layers) to a flattened "rootfs" tarball.
Why?
---
----
Docker images seems to be the lingua franca of distributing application
containers. It's hell convenient. But is it the best runtime environment? Not
for everyone.
containers. These are very wide-spread. However, is Docker the best runtime
environment? Not for everyone.
Undocker bridges the gap between image configurations and container runtimes:
now you can run a Docker image with systemd-nspawn and/or lxc.
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/or lxc, without doing the `docker pull; docker start; docker export` dance.
Usage -- extract docker image
-----------------------------
Download `nginx` docker image from docker hub and convert it to a rootfs:
```
skopeo copy docker://docker.io/nginx:latest docker-archive:nginx.tar
undocker rootfs nginx.tar - | tar -xv
```
(the same can be done with `docker pull` and `docker save`)
Usage -- systemd-nspawn example
-------------------------------
Once the image is converted to a root file-system, it can be started using
classic utilities which expect a rootfs:
```
systemd-nspawn -D $PWD nginx -g 'daemon off;'
```
@ -32,7 +39,7 @@ systemd-nspawn -D $PWD nginx -g 'daemon off;'
Usage -- lxc example
--------------------
Converting and creating the archive:
Preparing the image for use with lxc:
```
undocker rootfs nginx.tar - | xz -T0 > nginx.tar.xz
@ -40,7 +47,7 @@ undocker lxcconfig nginx.tar config
tar -cJf meta.tar.xz config
```
Importing it to lxc and running it:
Import it to lxc and run it:
```
lxc-create -n bb -t local -- -m meta.tar.xz -f nginx.tar.xz
@ -51,13 +58,17 @@ lxc-start -F -n bb -s lxc.net.0.type=none -- /docker-entrypoint.sh nginx -g "dae
Note: automatic entrypoint does not work well with parameters with spaces; not
sure what lxc expects here to make it work.
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
-------------
These are the contributions I will accept:
- pull requests for code.
- documentation updates.
I am very unlikely to react to bug reports (even if they are legit) without
accopmanying pull requests.
I will accept pull request for code (including tests) and documentation. I am
unlikely to react to bug reports without a patch.