[Buildroot] [All Systems Go!] Buildroot : Using embedded tools to build container images

[Esben Haabendal]

Arnout Vandecappelle <arnout at mind.be> writes:

> On 23/09/2019 09:44, Esben Haabendal wrote:
>> Peter Korsgaard <peter at korsgaard.com> writes:
>> 
>>>>>>>> "Arnout" == Arnout Vandecappelle <arnout at mind.be> writes:
>>>
>>> Hi,
>>>
>>>  >  Does this also work if the tarball is cross-compiled for a different
>>>  > architecture? Probably it does, and it just SIGILLs when you try to run the
>>>  > container...
>>>
>>> Yes. Even easier is just
>>>
>>> docker import output/images/rootfs.tar <myproject:mytag>
>>>
>>>  >  Yeah, except unfortunately docker security sucks, so on most distros you need
>>>  > sudo to run any docker command, even 'docker build'.
>>>
>>>  >  So, it would be nice if we could generate the OCI image without docker.
>>>
>>> I believe you can do similar with E.G. buildah:
>>>
>>> https://github.com/containers/buildah
>>>
>>> But you anyway need buildah/docker/.. to then finally do something with
>>> the docker image afterwards, so perhaps just documenting the 'docker
>>> import' oneliner is enough and not try to do it Buildroot.
>> 
>> Sorry for the duplicate comment about buildah.
>> 
>> To do something with an OCI image build with buildah, you should
>> consider using podman (https://github.com/containers/libpod), as it also
>> can be used without root priveleges, so should be feasible on shared
>> servers.
>
>  I may be wrong, but as I understand it, all these tools actually call docker
> under the hood.

You are wrong.  Buildah and Podman does not call docker in any way.

> They can be used without root privileges because they are
> installed with all the necessary suid bits and caps and stuff.

No suid bit.

> However, AFAIU, you can't build and install them as non-root and then
> create an image with it.

System must be configured to allow normal users to run unprivileged
containers (sysctl kernel.unprivileged_userns_clone=1).  Setting this
naturally requires privileges.

>  umoci was the only tool I found that seemed to *really* not require
>  root.

I suspect that there might some restrictions on what is possible when
using umoci as an unprivileged user (see
https://umo.ci/quick-start/rootless/).

/Esben