The 21st of March one my server stopped working without any apparent reason, and it could no longer reach the DNS server to lookup domains, so all the API calls made by my app started failing.
After excluding networking issues (pinging from console was working fine), and after a lot of digging I found out that the source of the error was actually a security patch just released by Canonical that caused NSS ABI to break after a few hours of running. This would result in being unable to reach any external domain, and the only solution would be to restart the server.
Thankfully they just released a patch of the patch so hopefully everything should be fine now.
I just find it amazing how something like that could have happened and how installing critical and recommended patches now has become something more like a roulette than a sense of relief.