Hi,
I know this is quite impossible to diagnose from afar, but I came across the posting from lemmy.world admins talking about the attacks they are facing where the database will get overwhelmed and the server doesn't respond anymore. And something similar seemed to have happened to my own servers.
Now, I'm running my own self-hosted Lemmy and Mastodon instances (on 2 seperate VPS) and had them become completely unresponsive yesterday. Mastodon and Lemmy both showed the "there is an internal/database error" message and my other services (Nextcloud and Synapse) didn't load or respond.
Login into my VPS console showed me that both servers ran at 100% CPU load since a couple of hours. I can't currently SSH into these servers, as I'm away for a couple of days and forgot to bring my private SSH key on my Laptop. So, for now I just switched the servers off.
Anyway, the main question is: what should I look at in troubleshooting when I'm back home? I'm a beginner in selfhosting and I run these instances just for myself and don't mind if I'd have to roll them back a couple days (I have backups). But I would like to learn from this and get better at running my own services.
For reference: I run everything in docker containers behind Nginx Proxy Manager as my reverse proxy. I have only ports 80, 443 and 22 open to the outside. I have fail2ban set up. The Mastodon and Lemmy instances are not open for registration and just have 2 users each (admin + my account).
Lemmy has the disadvantage of being opensource. In the long run this can be good for security but in the short term this gives your enemies a blueprint of your software and they know exactly how to attack you.
The only time I have every been compromised was when I was running 3rd party code open to the internet. I have been running my own code open to the internet for 20+ years and have been safe with it. I don't think I am some kind of god coder or anything but I am mindful of best practices and most importantly I am a small fish in a big pond.
Long story short is that running popular 3rd party code open to the internet exposes you to unique threats that you should be prepared for. Subnet/vlan it, vpn it, lock it down,