Lxd init --preseed < lxd.seed fails in untended curtin installation

LXD
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1

On Ubuntu 20.04 using MAAS + curtin + ansible to deploy servers, the following command fails only when in this setup.

# ensure lxd snap package is fixed to 4.17/stable
snap refresh --channel=4.17 lxd
cat << EOF > /etc/lxd.seed
config: {}
cluster: null
networks:
- config:
    ipv4.address: auto
    ipv6.address: none
  description: ""
  managed: false
  name: lxdbr0
  type: ""
storage_pools:
- config:
    size: 300GB
  description: ""
  name: default
  driver: zfs
profiles:
- config: {}
  description: ""
  devices:
    eth0:
      name: eth0
      nictype: bridged
      parent: lxdbr0
      type: nic
    root:
      path: /
      pool: default
      type: disk
  name: default
EOF

# following command executed via ansible-pull
/snap/bin/lxd init --preseed < /etc/lxd.seed

results in:

internal error, please report: running \"lxd\" failed: cannot find installed snap \"lxd\" at revision 21029: missing file /snap/lxd/21029/meta/snap.yaml

full Ansible shell output:

/snap/bin/lxd init --preseed < /etc/lxd.seed && touch /etc/lxd.init", "delta": "0:00:00.033602", "end": "2021-08-16 13:21:35.655923", "msg": "non-zero return code", "rc": 46, "start": "2021-08-16 13:21:35.622321", "stderr": "internal error, please report: running \"lxd\" failed: cannot find installed snap \"lxd\" at revision 21029: missing file /snap/lxd/21029/meta/snap.yaml", "stderr_lines": ["internal error, please report: running \"lxd\" failed: cannot find installed snap \"lxd\" at revision 21029: missing file /snap/lxd/21029/meta/snap.yaml"

when login for debugging the server, the snap refresh did work fine as I get the proper version:

lxd --version
4.17

Is there something which prevents from lxd init --preseed from a chroot during MAAS curtin installation? shall one use lxd init --auto instead? are there some conflicts with cloud-init and installing LXD as late curtin command?

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2

That error is coming from snapd and suggests that the snap isn’t properly functioning, indeed most likely caused because of you interacting with it from within a chroot.

snapd relies on systemd to handle its mounts, so in this case, I’d guess /snap/lxd/… isn’t mounted, causing the error.

I’m not familiar with this use of cloud-init and curtin, but maybe there’s a way for it to install and configure LXD on first boot instead of through a chroot during the installation?

As an alternative you could probably script your way around that lack of systemd by locating the right snap squashfs in /var/lib/snapd and manually mounting that over /snap/lxd/REVISION, then unmounting it after doing the configuration, but that feels very hackish.

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3

Thanks for the hints, postponing the lxd init --preseed with the following cloud-config in /etc/cloud/cloud.cfg.d/99_lxd-init.cfg did the trick.

#cloud-config
runcmd:
 - '/snap/bin/lxd init --preseed < /etc/lxd.seed'

I also checked cloud-init LXD module, yet it does not support storage pool size so rely on this runcmd: for the time being.