[Bug 2080892] Re: MAAS requires debconf for cloud-init preseed on Ubuntu

[Javier Fuentes]

** Changed in: maas
    Milestone: 3.6.x => 3.7.x

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Title:
  MAAS requires debconf for cloud-init preseed on Ubuntu

Status in MAAS:
  Triaged
Status in cloud-init package in Ubuntu:
  Triaged
Status in curtin package in Ubuntu:
  New

Bug description:
  MAAS uses curtin to create a cloud-init configuration using curtin's
  debconf_selections. Cloud-init's postinst script generates the preseed
  configuration based on debconf settings.

  This design is undesirable for several reasons:

  1. this design unnecessarily requires a distro-specific dependency: debconf
  2. this design unnecessarily requires that a duplicate implementation exist in MAAS for Ubuntu core[1][2] and other distros
  3. this design obscures project boundaries by hiding MAAS / curtin functionality in cloud-init's packaging shell scripts[3][4]

  It would be preferable to use the same (distro-agnostic) method
  everywhere. This code path already exists for non-Ubuntu distros and
  (if it works) would be much preferable to use everywhere.

  This would reduce maintenance burden:

  1. it will eliminate duplicate code paths[5]: which may diverge over time
  2. it will eliminate hacky shell postinst logic : this would be better implemented in a more maintainable repo/language
  3. it will clarify project boundaries and ownership of functionality: this functionality cannot currently be verified by the cloud-init team[6] - a cloud-init devel release is required, followed by MAAS CI runs

  [1] https://github.com/canonical/maas/blob/5f6f9d61ae3638c8fa89d0c73e0368a55145667c/src/maasserver/preseed.py#L154
  [2] https://github.com/canonical/curtin/blob/a5e8e4ad5c600af9f95e2cecf644d824ca0489e2/curtin/commands/curthooks.py#L1858
  [3] https://github.com/canonical/cloud-init/blob/ubuntu/devel/debian/cloud-init.postinst#L54
  [4] https://github.com/canonical/cloud-init/issues/5685
  [5] https://github.com/canonical/cloud-init/issues/5685#issuecomment-2342036576
  [6] https://github.com/canonical/cloud-init/issues/5688

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