Today, like the past few days, we have had some downtime. Apparently some script kids are enjoying themselves by targeting our server (and others). Sorry for the inconvenience.
Most of these 'attacks' are targeted at the database, but some are more ddos-like and can be mitigated by using a CDN.
Some other Lemmy servers are using Cloudflare, so we know that works. Therefore we have chosen Cloudflare as CDN / DDOS protection platform for now. We will look into other options, but we needed something to be implemented asap.
For the other attacks, we are using them to investigate and implement measures like rate limiting etc.
If your instance uses Cloudflare, then you have nothing to worry about, as your admin clearly has federation working. You wouldn't be posting here if they didn't.
I would assume improper configurations on the part of the admin. I've never tried setting up Lemmy, but if I had to take a wild guess people aren't configuring the SSL right and other instances aren't talking to them because the domain on the cert is wrong.