I noticed an error that occasionally occurs: Blacklists cannot be downloaded from a nethserver, thats why it notifies us about with an email. The source of this problem has nothing to do with the nethserver as it seems that the pihole which responds to dns requests stopps answering them, thus in nethserver I see one or more dns servers are not responding message in general settings tab. Now I certainly could just add a second dns server, but that would not eliminate the source of the problem.
Looking into the pihole box, I see that itself is still able resolve dns from console. But apparently there is a problem with pihole-FTL service. /var/log/pihole-FTL.log states that the database is not available and systemctl status pihole-FTL says that it’s active (exited).
Restarting said service brings back the dns resolving, but I’d like to know how to fix permanently in order to stop this intermittend failure.
No, I use a ProxMox VM with debian installed. Lately I decided to also install coturn on it to have our own stun/turn server for nextcloud talk. Comparing the vm specs after what you said with a second vm with another pihole, I also start thinking, that it could be because of limited ressources. I only gave 512 MB RAM to that VM and a 16GB hd (which should be enough, 2.4GB used) while on the other pihole VM I had assigned 1 GB of RAM. So maybe RAM is insufficient. I guess, I’ll try with doubling RAM or maybe even allocate 2GB given that it also serves as stun/turn server and see where it gets.
Unfortunatelly I don’t see where the db log is.
In ftl log shortly before it stopped answering dns queries I see:
Notice about db size being ~65MB
Reloading dns cache
db query called but db not available
I will report back and add solution if the problem will not occur within the next 2-3 weeks.