Re: "guix pack -f docker" does too much work

[Maxim Cournoyer]

Hi,

Ludovic Courtès <ludo@gnu.org> writes:

> Hi,
>
> Ricardo Wurmus <rekado@elephly.net> skribis:
>
>> a few months ago "guix pack -f docker" was modified to produce layers.
>> This is great!  Unfortunately, "guix pack" itself still produces one big
>> tarball containing all these layers.  There is no sharing of previously
>> built layers, because they are all hidden inside the pack.
>
> Right.
>
>> I think it would be great if "guix pack -f docker" could avoid building
>> all these identical layers again and again.  Perhaps it would be
>> possible to have a single derivation for each layer?  This way we
>> wouldn't have to recreate the same layer archives every time.
>
> That sounds nice in terms of saving CPU time.  It’s less nice in terms
> of disk usage: a single ‘guix pack -f docker’ run would populate the
> store with roughly twice the size of the closure.
>
> I think each solution (single derivation vs. one derivation per layer)
> makes a different tradeoff.  I don’t have a strong feeling about which
> one is better.

In past discussions (such as the implementation of the 'RPM' pack
format) we had concluded that a single derivation was preferable.  Large
chunks to be sent to offload machines over the network are not very
practical, and as Ludovic said, they also require more store space.

-- 
Thanks,
Maxim