Core DNS

Coredns ships by default with k3s, so it gets installed, but not really by anything we do by default 😅

Troubleshooting networking issues with coredns

Can your pod not get out to the internet? Well, first verify that it isn't the entire cluster with this:

kubectl run -it --rm --image=infoblox/dnstools:latest dnstools

Check the /etc/resolv.conf and /etc/hosts that's been provided by coredns from that pod with:

cat /etc/resolv.conf
cat /etc/hosts

# also check if this returns linuxfoundation's info correct
# cross check this with a computer that can hit linuxfoundation.org with no issues
host linuxfoundation.org

If it doesn't return linuxfoundation.org's info, you should first go read this k3s issue (yes, it's present in KIND as well).

Then decide, "does having subdomains on my LAN spark joy?"

Yes it sparks joy

And then update your ndot option in your /etc/resolv.conf for podDNS to be 1. You can do this in a deployment. You should read this k8s doc to learn more. The search domain being more than 1-2 dots deep seems to cause all sorts of problems. You can test the resolv.conf with the infoblox/dnstools docker image from above. It already has the vi text editor, which will allow you to quickly iterate.

No, it does not spark joy

STOP USING MULTIPLE SUBDOMAINS ON YOUR LOCAL ROUTER. Get a pihole and use it for both DNS and DHCP. Message brought to you by two engineers who lost a day to troubleshooting this.