[Bug 2051572] Re: Always preseed core and snapd snap in server seed

[Philip Roche]

> * boot times w/ and w/o preseeded snaps

Without preseeded snaps:
```
ubuntu at cloudimg:~$ systemd-analyze
Startup finished in 3.609s (kernel) + 11.026s (userspace) = 14.636s 
graphical.target reached after 10.642s in userspace.
```

With preseeded snapd and core22 snaps:

```
ubuntu at cloudimg:~$ systemd-analyze 
Startup finished in 3.733s (kernel) + 12.566s (userspace) = 16.300s 
graphical.target reached after 12.175s in userspace.
```

This is on a powerful AMD threadripper machine using qemu. I ran this 3
times for each image with similar results so we are definitely seeing a
boot speed improvement without the snaps preseeded.

I will try with only snapd snap too for comparison.

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https://bugs.launchpad.net/bugs/2051572

Title:
  Always preseed core and snapd snap in server seed

Status in ubuntu-meta package in Ubuntu:
  New
Status in ubuntu-meta source package in Noble:
  New

Bug description:
  In removing the LXD snap from preseeding in the server seed for Ubuntu
  24.04 as part LP #2051346 [1] we also removed the snapd snap and the
  core22 snap.

  This means that are subsequent snap install, like LXD, will take much
  longer than expected for a non minimized image.

  Time taken to install LXD snap using the lxd-installer package without
  snapd and core22 preinstalled/seeded

  ```
  ubuntu at cloudimg:~$ time sudo lxd --version
  Installing LXD snap, please be patient.
  5.19

  real	0m29.107s
  user	0m0.006s
  sys	0m0.005s
  ```

  Time taken to install LXD snap using the lxd-installer package with
  snapd and core22 already installed.

  ```
  ubuntu at cloudimg:~$ time sudo lxd --version
  Installing LXD snap, please be patient.
  5.19

  real	0m15.034s
  user	0m0.005s
  sys	0m0.005s
  ```

  This is a significant difference and for a workload we intend to
  remain as a core tested and tracked workload. As such I propose we re-
  introduce core22 and snapd snaps to our seed.

  LXD do intend to move to the core24 snap as their base as I'm sure
  snapd does too so when that does happen we need to update the
  preseeded core snap.

  This bug is to track the work of making that change in the server seed
  @ https://git.launchpad.net/~ubuntu-core-dev/ubuntu-
  seeds/+git/ubuntu/tree/server#n69

  [1] https://bugs.launchpad.net/ubuntu/+source/ubuntu-meta/+bug/2051346

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