I am currently out of town, and my server went down. All my services go through nginx, and suddenly started giving error 502. My SSH won’t let me in. I had my sister reboot the server, and it still doesn’t work. I apologize for the lack of details, but that is all I know, and I can’t access logs. I’ve cleared cache, and used a VPN in case fail2ban got me. I recently got a tp link router, so it could be something with that, but it was working for a while. I will have her do another reboot, and if that doesn’t work I will have her power off and unplug the server in case it was hacked.
Edit: I have absolutely no clue why, but it works now. I literally did nothing. As far as I know, my sister hasn’t touched it today. It just started working. Computers, man…
Edit 2: Actually she said she did something. Not sure what, but it works now.
Connection closed means somebody is listening to the port and failing/not willing to reply.
Unless some network middlemen is closing your connection (ssh should be on port > 1024 to be safe from ISP throttling), your ssh server is severely strained (oom, disk full…) or your F2B is kicking in.