The backend has crashed on a concurrency issue: https://gitlab.torproject.org/tpo/anti-censorship/rdsys/-/issues/234
I restarted it and seems to be back. But I'll find the source of the problem.
Quoting alertmanager@hetzner-nbg1-02.torproject.org (2024-09-23 06:25:51)
Total firing alerts: 1 Total resolved alerts: 0
## Firing Alerts
Time: 2024-09-23 04:25:21.784 +0000 UTC Summary: Exporter job metrics-standard on rdsys-backend.torproject.org:443 is down Description: Exporter job metrics-standard on rdsys-backend.torproject.org:443 has been unreachable for more than 15 minutes.
##Resolved Alerts