Re: Unreproducible «When Docker images become fixed-point»?

[Ludovic Courtès]

Hi,

zimoun <zimon.toutoune@gmail.com> skribis:

>> A possible reason why we’re building a different derivation than back
>> then is provenance info: as explained under ‘--save-provenance’ in the
>> manual, provenance info is not “canonical” and we could end up including
>> different provenance info.  I don’t have any clear scenario in mind but
>> that sounds plausible.
>
> I do not understand why provenance is not deterministic.  I mean I
> understand that two provenances can build the same pack, but I miss why
>
>         guix time-machine -C channels.scm \
>              -- pack -f docker --save-provenance -m manifest.scm
>
> is not building the same pack for the exact same channels.scm and
> manifest.scm files.  Why the resulting provenance info should be
> different?

I don’t know either, but that’s the only plausible scenario I can think
of.  We would need the original .drv or the original pack to compare.

> Maybe there is bug in how the provenance is managed; but I do not think
> it comes from this part.  Instead, I vaguely think the bug is from
> elsewhere – dependent on filesystem or unsorted list or other creative
> ideas. :-)

No, no: the store file names differ.  That means we’re building
different derivations in the first place.

> Well, let save some data, replay this scenario 6 months later and
> investigate. :-)  Keep you in touch.

Yeah.

Another approach is to take the derivation returned by

  guix time-machine --commit=fb32a38db1d3a6d9bc970e14df5be95e59a8ab02 -- \
    pack -f docker --save-provenance python python-numpy -d

and to look for things that might vary between invocations or call
sites: provenance data, imported modules, (guix config) details,
whatever.

Thinking about it, (guix config) is one possible source of discrepancy:
it captures sysconfdir and localstatedir, so you’ll get a different
result if you have different settings.  The defaults are:

  (define-public %localstatedir "/var")
  (define-public %sysconfdir "/etc")

Could it be that you had something different back then?

Ludo’.