It reminds me of a level of Serious Sam – the one where 1,000s of those headless bomb-toting zombie-soldiers and screamers came pouring at you relentlessly, seemingly to infinity (and beyond).
It was a backdraft. Or the eye of the Zombie-Nado-Cane. When the bad-bots got some air around August 5th – hak4umz.net DDoS or DNS Amplification – fail2ban (and the servers) got burned.
Even the “eye-dee-keff-kuh-may” (TammyBelle’s God Mode Code for DOOM][ ) cheat didn’t help. fail2ban got clobbered… ‘already banned’ every one second in the log and no more bans happening because 100s or 1000s of times per second from 100s or thousands of bots: bad requests.