Pihole Prometheus

Pihole and Prometheus

Pihole is a great DNS sinkhole to block ads on a local network. It’s web interface has great dashboards but exposes this data in a plain text key value format. I utilize prometheus and graphite for metric logging and visualize the data in grafana, all hosted in kubernetes, and I wanted to ingest pihole’s metrics into this ecosystem.

In my research, I found a pihole exporter which is referenced a fair amount by other guides and has great community reception. I however did not want to use a middleware service and would prefer a service (pihole) expose metrics directly. I decided to built a metrics endpoint directly into pihole’s web interface that can be directly scraped by prometheus.

Overview of changes.

For basic functionality, I added a new metrics.php file in the pihole’s lighttdp directory (/var/www/html/admin). The php file calls the api FTLAPI(‘stats’), which returns an array of metrics, and formats the output to Prometheus’s exposition format. This alone was sufficient for prometheus to scrape the pihole directly but I wanted to be able to toggle the metric’s page from the UI. I added a section in the settings.php file and a corresponding function in scripts/pi-hole/php/savesettings.php which toggled a setupvar. I lastly added a function in pihole’s /opt/pihole/webpage.sh script to manage a new Key Value variable METRIC_PAGE_ENABLE.

Proposing upstream changes

I wanted to propose these changes to the upstream pihole project but while reviewing feature requests in the pihole discourse I found this announcement for the v6 release. The main developers are moving away from lighttdp and have the pihole-FTL binary handle the web processing. As the main developers are focused on releasing v6, I have decided to wait for the release before reimplementing this for use in the pihole-FTL binary. For those who want to utilize this themselves, I have released my changes here with installation instructions for pihole v5.