Prometheus developer here. To make it highly available, just run two identical Prometheus servers. That way if either fails the other is still sending alerts,

Prometheus developer here. To make it highly available, just run two identical Prometheus servers. That way if either fails the other is still sending alerts, and if both are working the Alertmanager will automatically deduplicate the alerts. As for networking, we recommend running Prometheus on the same network as what it's monitoring to avoid crossing failure domains. You could also open up whatever ports you need on the firewall, just as you would for any other application. Prometheus is no different from any other monitoring solution in requiring firewalls to allow it's traffic through.