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

[Philip Roche]

With only snapd snap preseeded I get boot times very similar to

```
ubuntu at cloudimg:~$ systemd-analyze
Startup finished in 3.757s (kernel) + 12.458s (userspace) = 16.216s 
graphical.target reached after 12.061s in userspace.
```

Which shows we are still taking a boot time hit of ~1.5 seconds...
however with snaps snap preseeded we are seeing a much faster "first
snap" install. From ~21 seconds down to 17 seconds.


To summarise.

* Definitely faster boot without any snaps preseeded @ ~1.5 seconds in my tests
* Still slower boot with only snapd snap preseeded but faster first snap install time by about ~4 seconds

I have been unable to get any data on LXD usage numbers on cloud/server
to help.

So the question remains do we want faster boot by ~1.5 seconds (based on
my test environment) at the expense of first snap install speed
improvements of between 4 (if only snapd snap is preseeded) seconds and
up to ~15 seconds (if a core snap is also preseeded)?

@vorlon @jchittum @paelzer given the above findings are you still -1 on
any snap preseeding? Based on the data, I vote not to preseed any snaps.

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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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