guix pack: support for something similar to Nix's buildLayeredImage

[Simon Pugnet]

Hi,

I have been experimenting with using guix pack to build images.

Take the following examples: -

1. guix pack -f docker coreutils
2. guix pack -f docker python
3. guix pack -f docker coreutils python
4. guix pack -f docker rust
5. guix pack -f docker coreutils rust

If I then import those three (via "docker load < (store path to 
pack)") I see the following Docker images: -

1. coreutils                                           latest 
0ea7b529fa11   53 years ago    99.3MB
2. python                                              latest 
b6ff62311ffe   53 years ago    234MB
3. coreutils-python                                    latest 
17b7d53c54f1   53 years ago    255MB
4. rust                                                latest 
71c34a198b4a   53 years ago    1.05GB
5. coreutils-rust                                      latest 
96398a0a9efd   53 years ago    1.07GB

Inspecting those images shows that they each have only a single layer: 
-

1. "Layers": 
["sha256:0a82bb2a1af9a9e0f5c9ee48c0d103890bf520cf5fceb82be16d14f38f76c351"]
2. "Layers": 
["sha256:bdf366b7105cddb8c0fecded8a41f9d34389b2d19cb7c5e0b7760bd550f83d3a"]
3. "Layers": 
["sha256:361dae9e271d6ab0195ef3f8f338e03ec5114097e373197b73986ebc6bdf6cf1"]
4. "Layers": 
["sha256:64cb9e95374bdcd92034ad4956160ba4855f6e092b43a77ec38e1f8c5e4caad5"]
5. "Layers": 
["sha256:6c41ed1574777cd49d25e48d78d4e9070d9549c5c263f9f708af2c7e9f05f357"]

Examining the image storage directories for each shows them to have 
the following sizes (in bytes): -
1.   99349355
2.  234345507
3.  255198424 (~20MB larger)
4. 1046735591
5. 1067588316 (~20MB larger)

The problem with this is that for example the coreutils-python image 
contains coreutils as does any other image that happens to use 
coreutils like the example coreutils-rust. Examining the actual 
coreutils directory size in each image 
(/gnu/store/yr39rh6wihd1wv6gzf7w4w687dwzf3vb-coreutils-9.1) shows that 
it's 17131414 bytes in size, which corresponds approximately to the 
size increase I'm seeing in coreutils-python and coreutils-rust.

I'm not a Guix or Nix expert but as far as I understand Nix solves 
this problem by using "pkgs.dockerTools.buildLayeredImage" (see 
http://ryantm.github.io/nixpkgs/builders/images/dockertools/#ssec-pkgs-dockerTools-buildLayeredImage) 
and "streamLayeredImage". In this example, this could in theory be 
used to build a coreutils-python image where coreutils exists in its 
own layer. That would mean that the coreutils-rust image could share 
the coreutils layer, saving space.

Is there any way to achieve something similar in Guix? If not then are 
there any plans to support this functionality?

Kind regards,

--
Simon Pugnet
https://www.polaris64.net/
PGP key fingerprint: 3BF7 85DE 162C 00C8 FB4D  A6FD BA13 59A8 2C0B 
3EF9

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