I’m using ZeroTier on systemd-nspawn containers. Without ZT they boot up in about 400ms. Enabling ZT increases this to 13s. I have changed the systemd-networkd-wait-online.service so it doesn’t wait for all network interfaces. If it does, the boot time increases to 35s.
Disabling ipv6 support from the host OS and the container decreased the startup time to some 6s, which is ok. systemd-analyze critical-chain shows systemd-networkd-wait-online.service @145ms +5.997s. I don’t know how much of it is related to ZT…