I’m a network guy, so everything in my labs use SNMP because it works with everything. Things that don’t support SNMP are usually replaced and yeeted off the nearest bridge.
For that I use librenms. Simple, open source, and I find it easy to use, for the most part. I put it on a different system than what I’m monitoring because if it shares fate with everything else, it’s not going to be very useful or give me any alerts if there’s a full outage of my main homelab cluster.
Of course, access from the internet to it, is forbidden, and any SNMP is filtered by my firewall. Nothing really gets through for it, so I’m unconcerned about it becoming a target. For the rest of my systems security is mostly reliant on a small set of reverse proxies and firewall rules to keep everything secure.
I use a couple of VPN systems to access the servers remotely, all running on odd ports (if they need port forwards at all). I have multiple to provide redundancy to my remote access, so if one VPN isn’t working due to a crash or something, I have others that should get me some measure of access.