A number of people have touched on the perimeter security, but you can also look at your internal network too and whether you have the systems being exposed on vlans with firewalls preventing connectivity from those systems back to your other stuff that doesn’t need to be exposed. Could help cover you if a system is compromised due to bad config, zero day exploit, or whatever, by limiting the ability to then go sideways through your network to exploit other systems. Depending on what you are hosting there may be zero requirement for your externally facing server to need to talk to the majority of devices on your network, or the talk could be one way only (internal facing to external facing).