PiHole is working and blocking ads. I was migrating servers and noticed the following message in syslog
Pihole service is running on a docker container and the host is running Debian Bookworm. Following message was in journalctl and repeats periodically.
Dec 17 09:25:06 titan dockerd[850]: time="2024-12-17T09:25:06.550453472-06:00" level=error msg="[resolver] failed to query external DNS server" client-addr="udp:172.19.0.12:38538" dns-server="udp:192.168.1.86:53" error="read udp 172.19.0.12:38538->192.168.1.86:53: i/o timeout" question="
I used nc to see if I could identify any differences. Not sure if this is the best way.
From within a container i noticed UDP port was slow.
# from within docker containers udp is slow.
time nc -zv 192.168.1.86 53
Connection to 192.168.1.86 53 port [tcp/*] succeeded!
real 0m0.003s
user 0m0.000s
sys 0m0.003s
time nc -zvu 192.168.1.86 53
Connection to 192.168.1.86 53 port [udp/*] succeeded!
real 0m3.004s
user 0m0.004s
sys 0m0.000s
Same command when run from the docker host itself work fine. So i tried running pihole with host networking and I saw the same behavior. I am going to try macvlan and see if it changes anything. However if host mode is not showing any changes then I am not sure maclvan will be any better.
Also another interesting thing I noticed is that when running these commands from a host other than docker host I saw the same thing. Earlier I was assuming this had something to do with docker networking. Not it seems like its not docker that's causing this issue.
I tried nslookup commands and they are returning fast. I think nslookup defaults to udp. Both these points now lead me to think its not docker thats the issue.
Any pointers on what the cause of the timeout in the system log? Or should I just ignore it :).