Ask HN: How do I stop a DDoS attack?

A site I made/more or less passively admin (https://secrethitler.io) has been under a DDoS attack from some guy from eastern europe for about a week.

Because he's an idiot we have his real life name, university he goes to in Serbia, and of course his ISP ips and VPN ips, but nothing my moderators have tried seems to get this to end like emailing various people and then not getting responses.

Its pretty surprising that in 2021 some dude can somehow set up something equivalent to ping -f x100 or whatever and can take down a normal boring web app for a week+. A mod set up the usual "we are checking this browser" Cloudflare mitigation, along with manual nginx rules, etc, but none of that seemed to work.

Any suggestions would be great. Thanks!