prometheus-sd-nexthop is a tool that dynamically takes a Linux host's gateway IP addresses and presents them to Prometheus's HTTP service discovery functionality.

It is intended to be used alongside blackbox_exporter¹ on a Linux-based router to monitor the availability of the equipment belonging to a user's ISP.

Configure Prometheus as follows to have the router-nexthop job dynamically get IP addresses to probe from this service discovery tool (which listens on port 9198 by default) - and probe them with the blackbox_exporter prober:

- job_name: prometheus-sd-nexthop
  targets:
  - 10.0.0.1:9198
- job_name: router-nexthop
  metrics_path: /probe
  params:
    module: [icmp]
  scrape_interval: 20s
  relabel_configs:
  - source_labels: [__address__]
    target_label: __param_target
  - source_labels: [__param_target]
    target_label: instance
  - target_label: __address__
    replacement: 10.0.0.1:9115 # blackbox_exporter's port
  http_sd_configs:
  - url: http://10.0.0.1:9198/ # This service discovery service

This tool also exposes its own metrics at the /metrics endpoint.