Re: guix docker on gitlab-ci

[Graham Addis]

Hi Worf,

Thanks for the response, see below.

On Mon, 29 May 2023 at 20:41, wolf <wolf@wolfsden.cz> wrote:
>
> On 2023-05-24 18:04:47 +0100, Graham Addis wrote:
> > Dear people,
> >
> > I tried to create a docker image to use in a gitlab-ci instance but it
> > failed because I couldn't use --entry-point="bin/sh -l -c" or
> > equivalent, basically the gitlab-runner complains that it can't run
> > binaries.
>
> Would this be better using just bin/sh for the entry point and passing the -l
> and -c as an arguments?

Probably, but I don't think that's an option in gitlab ci and anyway
it would be nice to support the docker options.

> > I've managed to get it working by making some changes to 
> > guix/scripts/pack.scm
> >
> > Adding a fn in docker-image, just before the call to
> > build-docker-image, to create a list from the string passed in from
> > --entry-point="bin/sh -l -c"
> >
> >             (define (make-docker-exec-form prefix value)
> >               (cond
> >                ((equal? value '())
> >                 '())
> >                ((equal? prefix '())
> >                 (string-split value #\space))
> >                (else
> >                 (let ((values (string-split value #\space)))
> >                   (cons
> >                    (string-append prefix "/" (car values))
> >                    (cdr values))))))
>
> If I read this right (sorry, still somewhat new to guile), you basically split
> the --entry-point argument on spaces and use those parts as separate values to
> invoke, is that correct?  If so, how would you pass a binary that has space in
> the name (joke example: `/bin/ba sh') into the entry-point?

Basically, yes, and you are right about the problem.

I looked through all the guix documentation I could find and the only
other place I saw that a list was passed in an option was for URLs and
they were separated by spaces.

> > And replacing the setting of entry-point in the build-docker-image call to:
> >
> >                                 #:entry-point (make-docker-exec-form
> > #$profile #$entry-point)
> >
> > The call to build-docker-image takes a list for entry-point, and it
> > all works fine as far as I can tell.
> >
> > Before I send in a patch, some questions:
> >
> > Am I missing something?
> >
> > Am I on the right track?
>
> In my opinion (which you are free to disagree with :) ), I think it would be
> better to either have /bin/sh as an entry-point (and pass -l -c as arguments
> when starting the container, if required) or create a wrapper script /bin/shlc
> that would exec /bin/sh with correct arguments.

Yep, lots of possible workarounds, but it seems to me that it would be
better spending the time adjusting the pack command to fit the spec.

> Few random ideas: Maybe the same format Containerfiles use for cmd and
> entrypoint directives could be used?  Maybe the --entry-point could also (in
> addition to a string) accept a list of strings (LISP list)?

Sounds good to me. Do you have a reference for the json for this? (Not
a big deal as I think I've worked it out from the code, but it's
always nice to have the specs...)

>From the Dockerfile reference for ENTRYPOINT
https://docs.docker.com/engine/reference/builder/#entrypoint there are
two fomrs:

ENTRYPOINT ["executable", "param1", "param2"] # The exec form, which
is the preferred form:

ENTRYPOINT command param1 param2 # The shell form:

To implement the shell form I'd need to update build-docker-image in
guix/docker.scm
https://git.savannah.gnu.org/cgit/guix.git/tree/guix/docker.scm#n139
to take a string instead of/ as well as the list it currently takes.
Then update docker-image in guix/scripts/pack.scm
https://git.savannah.gnu.org/cgit/guix.git/tree/guix/scripts/pack.scm#n592

Invocation would then simply be --entry-point="command param1 param2"

To implement the exec form (preferred according to docker) I wouldn't
need to touch guix/docker.scm, but I would probably need to change the
parsing for --entry-point as well as updating docker-iimge.

I prefer the second option, for which all I need is some guidance on
the option syntax

.e.g. --entry-point=["command", "param1", "param2"]

Suggestions please. :)

I could implement both and test for a string or a list and choose
between the shell and exec forms from there, but to be consistent with
the existing implementation.

Once I'm clear about the best approach for this, I could add the CMD
too, if that would be useful.
https://docs.docker.com/engine/reference/builder/#cmd

One strange thing, I couldn't see the need for prefixing the profile
to the ENTRYPOINT command:
https://git.savannah.gnu.org/cgit/guix.git/tree/guix/scripts/pack.scm#n670
I took it out and everything seems to work, so I'm not sure what
problem it is fixing. Anybody any idea?

Thanks,

Graham