First thing I always do on any new VPS is to sort out SSH (disable root login, disable password login), set up fail2ban, install and configure ufw... and if I need to set up something like redis or similar, make sure it only listens to internal connections and also that it is decently auth'd. For deployment and other things I make users that can only write to certain directories; no sudo. It's nothing new or special but it gets lost in distributed systems.

It's a lot more work when doing it in the cloud and spinning up these things from docker containers in K8S...but you're entirely to blame if you don't know what you're deploying and don't understand any of the potential threats.