Site was offline for ~2 days for maintenance, as I was moving the entire infrastructure to the new Server, which is located somewhere in the frosty north, and has plenty of hardware to handle the things I throw at it. For those on IPv6, the site should already be 100% online again, while for those on IPv4-only, it may take a day or so to update. During the move/maintenance I learned a couple things:

1. While the majority of ISPs have adopted IPv6 (some even being IPv6-only), there are still some that only have IPv4 or require IPv4 or their DNS won’t resolve the IPv6 addresses. It is baffling that 26 years after the standard has been accepted (~15 years for the adoption) that some ISPs are actually so incompetent to not have IPv6 support at all.
2. Because of the above, I now know how to forward ports to VMs without it only working one-way. I no longer have to buy more IPv4 addresses, which are already sparse enough, to allow those ISPs to keep working fine. Thanks to that ServerFault user for pointing me in the right direction.
3. As far as testing goes, a single 10gbit link seems to outperform any previous infrastructure I had. Even though the server is in the north which increases ping quite a bit, it is still responding much faster than when it was local to me. It’s also way easier to maintain now, as it’s 1 physical machine instead of 4 different ones.
4. SystemD is annoying and painful to work with. It will fight you with everything it has, even if you follow the documentation as stated. Especially systemd-resolved and systemd-networkd. Great if they work, awful if they don’t.
5. As expected, Zen1 to Zen3 is a massive upgrade even when used as a Server. All VMs are booting blazingly fast now, with the Database even having a 2-3x increase in raw throughput. Absolutely worth the extra 30€/mo if you ask me.
6. Debian is … questionable these days. ‘partman’ still doesn’t have any idea what KiB/MiB/GiB/… is, the installer still requires a normal user account for server installs, and for some reason there’s still bloat being installed in the netinst version.

And I’m also left with one question: What the heck do I do with 8 Zen3 cores that are practically sitting idle?!

Update: The mail server is now also available with IPv4 again, as people still pretend that IPv6 doesn’t exist. Notably affected are: Amazon, Microsoft, Google/YouTube, the FFmpeg mailing list, the Debian mailing list, Slack, and some others that I forgot the names of. Shame on every single one of the listed for not supporting IPv6 in 2021.