Self-Hosted Main

Alerts are much more important than fancy dashboards. You won't be staring at your dashboard 24/7 and you probably won't be staring at it when bad things happen.

Creating your alert set not easy. Ideally, every problem you encounter should be preceded by corresponding alert, and no alert should be false positive (require no action). So if you either have a problem without being alerted from your monitoring, or get an alert which requires no action - you should sit down and think carefully what should be changed in your alerts.

As for tools - I recommend Prometheus+Grafana. No need for separate AletrManager, as many guides recommend, recent versions of Grafana have excellent built-in alerting. Don't use those ready-to-use dashboards, start from scratch, you need to understand PromQL to set everything up efficiently. Start with a simple dashboard (and alerts!) just for generic server health (node exporter), then add exporters for your specific services, network devices (snmp), remote hosts (blackbox), SSL certs etc. etc. Then write your own exporters for what you haven't found :)