[Feature Request] Prometheus endpoint

[MaartenMol]

Add an /metrics endpoint so that Prometheus can scrape from it. This way we can choose what TSDB to use.

[dirtycajunrice]

adding an endpoint would require hosting a flask app and defining a port. This was not the design choice for us and was designed to pull information only, not be pulled from. I suggest you looking into the already existing integration built for this between prometheus_read and influxdb. https://docs.influxdata.com/influxdb/v1.7/supported_protocols/prometheus/

[dirtycajunrice]

Further knowledge has shown that the prometheus python module is fully capable of doing this. Re-opening and leaving for when either i have time or someone would like to attempt :D

[dirtycajunrice]

https://github.com/Boerderij/Varken/tree/prometheus-exporter WIP

[PrivatePuffin]

Slight addition: Someone informed me InfluxDB 2.0 also supports pulling Prometheus datasources, which means implementing this also de-facto solves #159