Nightly ISO images are regularly unavailable for a couple minutes

Reference: https://icingaweb2.tails.boum.org/monitoring/service/history?host=ecours.tails.boum.org&service=nightly_devel

IIRC I’ve reported this bug during the initial dev phase of the monitoring system, and we decided it wasn’t a bug in the monitoring system but in the actual service. So let’s fix the bug in the actual service then :)

Today the 1st occurrence of this problem in www.lizard nginx’ error.log is at 07:54:08. Yesterday it was at 07:54:17. On July 2 it was at 07:54:26, etc. I doubt that’s a coincidence, and I suspect we have a cronjob or something that breaks this stuff everyday or close to it (and then either our monitoring is fast enough to report it to us, or it’s not).

Original created by @intrigeri on 11557 (Redmine)