It used to be that each machine had one purpose. Your load balancer machines talked to your web server machines which talked to your database machines. Instrumentation from these systems didn’t tend to be spectacular, so the most practical approach was to rely on and page on machine metrics such as CPU. Sure it wasn’t perfect, but it caught most of the times the service got overloaded.
There’s the odd false positive.
Grafana is used by hundreds of thousands of users on a wide variety of data sources. Among these there is a division in approaches to collecting the data. These are logging as exemplified by Elasticsearch as part of the ELK stack (Elasticsearch, Logstash and Kibana), and metrics as exemplified by Prometheus.
What do I mean by monitoring? Monitoring means knowing what’s going on inside your system, how much traffic it’s getting, how it’s performing, how many errors there are.