I had setup a raspberry pi cluster, and suddenly the master became non-operational. The cluster was able to see itself, but if I login to master node, I noticed it was not able communicate externally.
The DNS Resolution for any site from master was failing.
Then I figured that Ubuntu had made some changes to resolve.conf protocol
Ubuntu requested users not to edit /etc/resolv.conf, and it's content on my cluster was not something that I wanted.
I had setup pihole, and my devices had started to see the internet through this. I noticed that Ubuntu since 18.04 had not set my router as the first nameserver and thus after pi-hole experiment, my master node lost its resolution capability
Fixing the Ubuntu DNS resolution was easy. I followed this post from datawookie
- resolvconf package was already installed.
- Edit /etc/resolvconf/resolv.conf.d/head
nameserver <pi-hole-server> nameserver 126.96.36.199 nameserver 188.8.131.52
- Restart the resolvconf server
sudo service resolvconf restart