Netcup DNS notes

[girish]

In Cloudron 8, we have switched the host DNS to use systemd-resolved (the ubuntu default) . unbound is still used but only for mail server and when we need to do recursive lookups.

In the process of testing with various VPS, I found some curious things in netcup servers. Just putting my notes here:

• Netcup makes /etc/resolv.conf non-editable for some reason (using chattr). They also put their nameservers there directly into resolv.conf instead of using netplan. Curiously, netplan does have the static IP, so they do know about netplan configs... Maybe something do with multiple interfaces? They could have used /etc/systemd/resolved.conf as well . Anyway, they have an unconventional setup.
• Ubuntu 20 servers has systemd-resolved running. But this is actually not used at all because resolv.conf is pointing to nameservers directly
• Ubuntu 22 servers are same as 20. systemd-resolved is running but unused.
• Ubuntu 24 servers have systemd-resolved disabled (ha, looks like someone noticed and corrected the problem here)

Cloudron install and update scripts patch up netplan and resolv.conf to use systemd-resolved. In the future, maybe we remove this netcup specific patch. Don't like maintaining VPS specific code especially when those things change without notice.