Prometheus is a highly capable monitoring tool that assembles metrics and pushes them to a consumer. It may be used for just about anything you could think of. It has quite big community that develops exporters for a number of projects. Nodejs, php, linux machines etc.
In my infrastructure I use node exporters for my bare-metal nodes, nodejs exporter for one of the apps and for the kubernetes cluster running inside of the VirtualBox vms. The consumer of the metrics is Grafana.
Prometheus instances are added as data sources in grafana
Kubernetes has its own prometheus instance running inside of the cluster and is added as another data source to grafana.
Prometheus targets may be observed through NodePort export to external ips of Nodes.
Grafana dashboard shows the kubernetes statistics.