I use systemd-nspawn to create test containers so I can muck with the internals without dealing with docker cp and exec commands. The containers themselves are just directories sitting in a filesystem.

I ended up writing a shell script to handle setting up a bridge, launching the container with systemd-nspawn and kick off commands to bring up the virtual ethernet interfaces inside the container and handle some other housekeeping

systemd-nspawn with systemd-network/resolve/etc can automatically manage the IP addresses for you. I'm using it as a wrapper around cgroup/netns commands.

One of these days, I will remove the dependency on systemd-nspawn so that I can use it on Linux systems without systemd or docker.