prometheus server cannot reach build-arm* boxes
build-arm-0[None..None](../compare/None...None).torproject.org boxes are behind NAT (or some sort of firewall?) which makes them unreachable from the global internet. They are therefore not monitored from the Prometheus server right now, although they are reachable from the Nagios server.
We need to setup a similar configuration to have those boxes scraped like the other ones.