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I've tried to add "nameserver 127.0.0.1" to "/etc/resolv.conf" instead, but then the coredns pods give me error logs indicating there is an infinite resolution loop (basically what's mentioned here https://coredns.io/plugins/loop/#troubleshooting)

You will probably need to use a dummy default route and dummy upstream DNS server that returns nxdomain or the like. Kubernetes can be used in an airgap configuration, but some of the iptables rules and other things will only work right if packets go through the normal routing process. So you can have an airgaped network without too much extra configuration, but an airgapped host takes more work.

Hi! thanks for your reply. We've tried that but nslookup still fail with "no servers could be reached" error.. Seems to be something else than dns resolution.

Did you add a dummy default route? All the stuff that routes to clusterip services won't work without it.

I tried to set up a dummy interface but no success.. i'm not sure i did it right, could you be more specific about how to do it please ? Sorry, I am not a network expert..

in your

/etc/netplan/<default file>.yaml

you need to add a dummy route, for example:

routes:
            - to: default
                via: 172.16.0.1

Or when installing ubuntu you can set this IP as the

gateway

when prompted go configure a network device