[Disco] Ubuntu Desktop fails to build - snap-tool download: failed to get details for 'core18' in 'stable/ubuntu-19.04' on 'amd64': No revision was found in the Store.

[Jean-Baptiste Lallement]

core18 has been seeded on Ubuntu Desktop minimal and since today builds are failing with:

+ SNAPPY_STORE_NO_CDN=1 /usr/share/livecd-rootfs/snap-tool download --cohort-key= --channel=stable core
renamed 'chroot/var/lib/snapd/seed/core_6531.assert' -> 'chroot/var/lib/snapd/seed/assertions/core_6531.assert'
renamed 'chroot/var/lib/snapd/seed/core_6531.snap' -> 'chroot/var/lib/snapd/seed/snaps/core_6531.snap'
+ cd chroot/var/lib/snapd/seed
+ SNAPPY_STORE_NO_CDN=1 /usr/share/livecd-rootfs/snap-tool download --cohort-key= --channel=stable/ubuntu-19.04 core18
snap-tool download: failed to get details for 'core18' in 'stable/ubuntu-19.04' on 'amd64': No revision was found in the Store.
If the channel (stable/ubuntu-19.04) includes '*/ubuntu-##.##' track per
Ubuntu policy (ex. stable/ubuntu-18.04) the publisher will need
to temporarily create the channel/track to allow fallback during
download (ex. stable/ubuntu-18.04 falls back to stable if the
prior had been created in the past).

ProblemType: Bug
DistroRelease: Ubuntu 19.04
Package: livecd-rootfs (not installed)
ProcVersionSignature: Ubuntu 4.19.0-13.14-generic 4.19.20
Uname: Linux 4.19.0-13-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.10-0ubuntu23
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Tue Mar 19 12:15:26 2019
InstallationDate: Installed on 2014-07-15 (1708 days ago)
InstallationMedia: Ubuntu 14.10 "Utopic Unicorn" - Alpha amd64 (20140520)
SourcePackage: livecd-rootfs
UpgradeStatus: Upgraded to disco on 2018-03-24 (359 days ago)

[Ken VanDine (ken-vandine)]

The stable/ubuntu-19.04 track has been created for core18, should fix this.

[Steve Langasek (vorlon)]

> The stable/ubuntu-19.04 track has been created for core18, should fix this.

As discussed on IRC, I don't think this is the right fix. We do NOT want a proliferation of core18 snaps on different per-Ubuntu-release branches with subtle differences; we expect the base snap to be a common base that works on all target classic releases and in support of all snaps using that base.

So the bug here is in livecd-rootfs not knowing to treat core18 specially. The images are building again, but they're building WRONG, seeding core18 from the stable/ubuntu-19.04 channel instead of the stable channel they should be using.

I also don't think the core18 snap belongs in the seed (where it has now been added). We do have to seed the gnome-3-28-1804 snap currently, and that does (and should) carry a per-Ubuntu-release branch, but I think base snaps should not have to be seeded directly for the same reason we don't manually seed all the dependencies of the leaf packages.

So I would like to see:

 - livecd-rootfs updated to know when it needs core18 as a base for one of the seeded snaps
 - livecd-rootfs to detect when *all* seeded snaps specify a base:, and if so, seed snapd instead of core
 - core18 removed from the seed.

[Tobias Koch (tobijk)]

I would like to propose this change to snap-tool to partially mitigate the problems discussed here:

https://code.launchpad.net/~tobijk/livecd-rootfs/+git/livecd-rootfs/+merge/364800

[Łukasz Zemczak (sil2100)]

Thanks Tobias! I have merged and released your changes, let's see how the nearest image builds go.

[Steve Langasek (vorlon)]

I've triggered a test build of the desktop ISO now so we can confirm it's doing what's expected with livecd-rootfs 2.576, but per Tobi this is not a complete solution per comment #3 and we cannot unseed core18 from the desktop seed (we need https://code.launchpad.net/~mwhudson/livecd-rootfs/+git/livecd-rootfs/+ref/no-snaps-ubuntu-cpc-minimized for that) so setting this back to 'in progress'.

[Łukasz Zemczak (sil2100)]

Yes, indeed this does not address the need of seeding core18, my bad that I didn't consider it as a primary issue. I guess the bug description here confused me, as it only mentioned the issue with the track being used. Let me follow up with an upload for that. What I'll propose is special-casing the snap-tool, since as per my comments in the MP, snap prepare-image --classic doesn't do auto-resolving of base as well currently.

[Łukasz Zemczak (sil2100)]

Thank you Tobias for the follow up fixes! I suppose this should do the job.

I have now also removed core18 from the disco seeds (a bit late in the process, but oh well). During the next release candidate images we should see if all works as expected and if both core18 and snapd snaps are preseeded. If, of course, none of the seeded snaps have core as the base.