node_exporter ( https://github.com/prometheus/node_exporter ) and process_exporter ( https://github.com/ncabatoff/process-exporter ) expose the most of the useful metrics needed for monitoring server infrastructure together with the running processes. I'd recommend also taking a look at Coroot agent, which uses ebpf for exporting the essential host and process metrics - https://github.com/coroot/coroot-node-agent .

As for the agent, it is better from operations perspective to run a single observability agent per host. This agent should be small in size and lightweight on CPU and RAM usage, should have no external dependencies and should have close to zero configs, which need to be tuned, e.g. it should automatically discover all the apps and metrics needed to be monitored, and send them to the centralized observability database.

If you are lazy to write the agent on yourself, then take a look at vmagent ( https://docs.victoriametrics.com/vmagent/ ), which scrapes metrics from the exporters mentioned above. vmagent satisfies most of the requirements stated above except of configuration - you need to provide configs for scraping metrics from separately installed exporters.