I was recently looking for an ultra minimal monitoring solution for OpenWrt and other lightweight systems (Pi’s, etc.) and was disappointed not to find one that met my needs (negligible CPU, disk space and RAM).
I ended up hacking together a shell script to send data to Home Assistant (via MQTT) which runs on pretty much any system that has at least netcat: https://github.com/roger-/hass-sysmon
why not use https://collectd.org/ which is in C and used by openwrt's luci already along with rrdtool, small in size, low on resource, and has so many plugins already?
Did you try VictoriaMetrics [1] and vmagent [2]? It is a single self-contained binary without external dependencies. It requires relatively low amounts of CPU, RAM, disk space and disk IO, and it runs on ARM.
I ended up hacking together a shell script to send data to Home Assistant (via MQTT) which runs on pretty much any system that has at least netcat: https://github.com/roger-/hass-sysmon