[moreentropy]

Well it just works and is extremely simple to use.

I usually debootstrap into /var/lib/machines/something and do "machinectl enable something; machinectl start something", that's it. Then I attach to the machine using "machienctl shell something" and configure networking (host0 interface) inside the domain, that's it.

For drop in configuration systemd-nspawn parses a config file /etc/systemd/nspawn/something.nspawn which usually just contains network configuration on my hosts:

[Network] Bridge=br-int

Systemd-nspawn enables and user namespacing by default and chowns the machines's root filesystem on first start. If that's not desired (Things like Samba fileservers don't work well with user namespacing) just disable it in the .nspawn file:

[Exec] PrivateUsers=no

Everything you need to know is in the manpages systemd-nspawn and systemd.nspawn. I usually install systemd from stretch-backports because running a fairly recent systemd version helps as it still gets new features, but I never had problems with stability.

[yupyup]

Great, sounds quite simple.

One thing I somewhat miss from what you are explaining is all the aditional things that LXD gets you (snapshots using ZFS, image publishing/sharing, migrating containers between LXD hosts...)

But maybe some of those things are still doable (e.g. mounting a ZFS dataset as storage for /var/lib/machines/containerX)...

Thanks for your answer!

[moreentropy]

Haven't dealt with live migration, but mounting filesystems should be easy using systemd's unit dependencies.

Just drop a .mount file in /etc/systemd/system and set RequiredBy=[e-mail] and StopWhenUnneeded=true and the filesystem should be mounted before the machine starts and unmounted when the machine is shut down. See the manpages systemd.unit and systemd.mount for details.