What is the required root host filesystem size for LXD?

What is a safely small filesystem size to use as the root filesystem on an LXD host?
Does it depend on the size of the containers? Does LXD store intermediate archive files on the root filesystem (e.g. in /tmp) when exporting containers or images, or for similar operations?

I’m considering installing Ubuntu 18.04 + snap LXD to a repartitioned Hetzner VPS, as described here: https://blog.simos.info/how-to-repartition-a-hetzner-vps-disk-for-zfs-on-its-own-partition-for-lxd/
Would 4GB be enough for the root partition?

4GB feels too small for your root filesystem.
I had a quick look at my LXD servers and their / ranges from 7GB to 15GB, they’re all LXD hosts, don’t have much else going on but have been up for several years.

LXD does keep all active images as tarballs in /var/snap/lxd/common/lxd/images, same goes for container backups. We do have pending work to change this though, at which point you’ll be allowed to select one of the storage pools for this.

When publishing a container or unpacking an image, this is also done in /var/snap/lxd/common/lxd/images or /var/snap/lxd/common/lxd/backups, so this may need enough room to hold an uncompressed copy of the container you’re publishing + the needed space for the compressed copy.

With that in mind, 15 to 20GB would be good. I tend to go with 20GB but my servers are physical servers with lots of storage, so it’s not a huge deal if I’m wasting a bit of space on /.