I have just concluded a post-mortem on one of my servers.
Cause of death: out of memory due to a tiny memory leak in a VPN service triggered by 66 different IPs brute-forcing the creds at the same time. Mostly from China, of course.

Dear bot writers: you made me put aside my spaghetti and write iptables rules. I hate iptables. And I love spaghetti. You should be ashamed of yourself! Did momma not teach you basic OpSec? Don't crash the target and never, ever, interrupt the sysadmin during dinner!