[Bug 2067425] Re: lxd-installer should default to pulling LXD from the $LTS/stable/ubuntu-XX.YY channel

[Denis Lalaj]

** Description changed:

- Since LP: #2061910, lxd-installer pulls LXD snap from `5.21/stable` for
- non LTS Ubuntu versions. This should be improved to pull from
- `$LTS/stable/ubuntu-XX.YY` as using a specific branch can be handy if we
- need to push an emergency fix to the Ubuntu release specific
- channel/branch.
+ [ Impact ]
+ 
+ Performing a snap install without --channel specified will pull the
+ latest version as it defaults to tracking 5.21/stable. For focal and
+ jammy images, this results into the installation of lxd version 5.21.
+ Selecting the channel based on the release is preferred to be able to
+ push fixes to the specific channel in cases of issues impacting an
+ individual release.
+ 
+ [ Test Plan ]
+ 
+ To reproduce the issue you can launch a minimal lxc container (example given for focal): `lxc init ubuntu-minimal-daily:focal test && lxc start test && lxc exec test bash`
+ Inside the container, if you run `snap install lxd`, you will see the snap listed as `lxd     5.21.3-c5ae129  33110  5.21/stable    canonical✓  -` which is being pulled from `5.21/stable`.
+ 
+ Repeating the same for jammy: `lxc init ubuntu-minimal-daily:jammy test && lxc start test && lxc exec test bash` gives the same result:
+ The snap is pulled from channel `5.21/stable`: `lxd     5.21.3-c5ae129  33110  5.21/stable    canonical✓  -`
+ 
+ The proposed changed allows the lxd-installer to fix the channel for focal and jammy respectively:
+ Focal: `lxd     4.0.10-d342340  32662  4.0/stable/…   canonical✓  -`
+ Jammy: `lxd     5.0.4-497fe1e  31333  5.0/stable/…   canonical✓  -`
+ 
+ [ Where problems could occur ]
+ 
+ Since the channel to track for the snap install is being fixed, any
+ future decision that could result in wanting focal or jammy to track a
+ different channel would require an update to reflect the channel being
+ tracked. Further, any fixes issued for the lxd snap on the 5.21/stable
+ channel will not become immediately available to the snap in focal or
+ jammy images, unless they are also needed for these releases in which
+ case the fixes should also be provided for the respective channels
+ `4.0/stable/ubuntu-20.04` and `5.0/stable/ubuntu-22.04`
+ 
+ However, focal and jammy images were originally seeded with LXD
+ 4.0/stable/ubuntu-20.04 (for focal) and 5.0/stable/ubuntu-22.04 (for
+ jammy); therefore fixing the channel aligns the installation of the snap
+ with how this was done for "older" images prior to the introduction of
+ the lxd-installer.
+ 
+ It is also reasonable to not expect all fixes for the 5.21/stable to
+ appear for focal/jammy images unless these releases are affected by the
+ issue like more recent releases.
+ 
+ Further, this service is what installs the snap but it does not prevent
+ later switching the channel of the snap on the instance; an end user can
+ always choose to move to a different channel.
+ 
+ [ Other Info ]
+ 
+ Selecting the lxd_channel is currently happening for lxd-installer in the devel branch based on the following. 
+ * 25.04 / 24.10 / 24.04 track channel 5.21
+ * 22.04 tracks channel 5.0
+ * 20.04 tracks channel 4.0
+ 
+ [Original Description]
+ Since LP: #2061910, lxd-installer pulls LXD snap from `5.21/stable` for non LTS Ubuntu versions. This should be improved to pull from `$LTS/stable/ubuntu-XX.YY` as using a specific branch can be handy if we need to push an emergency fix to the Ubuntu release specific channel/branch.

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https://bugs.launchpad.net/bugs/2067425

Title:
  lxd-installer should default to pulling LXD from the
  $LTS/stable/ubuntu-XX.YY channel

Status in lxd-installer package in Ubuntu:
  Fix Released
Status in lxd-installer source package in Focal:
  New
Status in lxd-installer source package in Jammy:
  New

Bug description:
  [ Impact ]

  Performing a snap install without --channel specified will pull the
  latest version as it defaults to tracking 5.21/stable. For focal and
  jammy images, this results into the installation of lxd version 5.21.
  Selecting the channel based on the release is preferred to be able to
  push fixes to the specific channel in cases of issues impacting an
  individual release.

  [ Test Plan ]

  To reproduce the issue you can launch a minimal lxc container (example given for focal): `lxc init ubuntu-minimal-daily:focal test && lxc start test && lxc exec test bash`
  Inside the container, if you run `snap install lxd`, you will see the snap listed as `lxd     5.21.3-c5ae129  33110  5.21/stable    canonical✓  -` which is being pulled from `5.21/stable`.

  Repeating the same for jammy: `lxc init ubuntu-minimal-daily:jammy test && lxc start test && lxc exec test bash` gives the same result:
  The snap is pulled from channel `5.21/stable`: `lxd     5.21.3-c5ae129  33110  5.21/stable    canonical✓  -`

  The proposed changed allows the lxd-installer to fix the channel for focal and jammy respectively:
  Focal: `lxd     4.0.10-d342340  32662  4.0/stable/…   canonical✓  -`
  Jammy: `lxd     5.0.4-497fe1e  31333  5.0/stable/…   canonical✓  -`

  [ Where problems could occur ]

  Since the channel to track for the snap install is being fixed, any
  future decision that could result in wanting focal or jammy to track a
  different channel would require an update to reflect the channel being
  tracked. Further, any fixes issued for the lxd snap on the 5.21/stable
  channel will not become immediately available to the snap in focal or
  jammy images, unless they are also needed for these releases in which
  case the fixes should also be provided for the respective channels
  `4.0/stable/ubuntu-20.04` and `5.0/stable/ubuntu-22.04`

  However, focal and jammy images were originally seeded with LXD
  4.0/stable/ubuntu-20.04 (for focal) and 5.0/stable/ubuntu-22.04 (for
  jammy); therefore fixing the channel aligns the installation of the
  snap with how this was done for "older" images prior to the
  introduction of the lxd-installer.

  It is also reasonable to not expect all fixes for the 5.21/stable to
  appear for focal/jammy images unless these releases are affected by
  the issue like more recent releases.

  Further, this service is what installs the snap but it does not
  prevent later switching the channel of the snap on the instance; an
  end user can always choose to move to a different channel.

  [ Other Info ]

  Selecting the lxd_channel is currently happening for lxd-installer in the devel branch based on the following. 
  * 25.04 / 24.10 / 24.04 track channel 5.21
  * 22.04 tracks channel 5.0
  * 20.04 tracks channel 4.0

  [Original Description]
  Since LP: #2061910, lxd-installer pulls LXD snap from `5.21/stable` for non LTS Ubuntu versions. This should be improved to pull from `$LTS/stable/ubuntu-XX.YY` as using a specific branch can be handy if we need to push an emergency fix to the Ubuntu release specific channel/branch.

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