Comment 28 for bug 1865515

By default an LXD VM boots from the disk first. However you can change the boot order by adding "boot.priority" to your devices. The device with the highest number boots first.

LXD devices config for booting off the boot disk.
devices:
  eth0:
    name: eth0
    nictype: bridged
    parent: br0
    type: nic
  root:
    path: /
    pool: default
    size: "8000000000"
    type: disk

LXD devices config for booting off the network first.
devices:
  eth0:
    boot.priority: "1"
    name: eth0
    nictype: bridged
    parent: br0
    type: nic
  root:
    boot.priority: "0"
    path: /
    pool: default
    size: "8000000000"
    type: disk