Tip: Pod FQDN in Kubernetes

Pods from deployment, statefulset. daemonset exposed by service

FQDN is  pod-ip-address.svc-name.my-namespace.svc.cluster.local

i.e  172-12-32-12.test-svc.test-namespace.svc.cluster.local

not 172.12.32.12.test-svc.test-namespace.svc.cluster.local

Isolated Pods:

FQDN is  pod-ip-address.my-namespace.pod.cluster.local

i.e  172-12-32-12.test-namespace.pod.cluster.local

Tip to Verify KubeDNS is Working From Host

Requirement:

Sometimes we need to verify KubeDNS is working from host OS( ie VM ).

Solution:

• Find KubeDNS service IP address via command

kubectl run -i --tty busybox --image=busybox --restart=Never -- cat /etc/resolv.conf

• install nc if necessary. ie yum install nc
•  ie the IP address is 10.96.5.5 , then run while loop to check each KubeDNS pod is responding. You may get timeout or can't resolve error if one of the pods is not working

while true;do nc -vz 10.96.5.5 53;sleep 3; done

• More debug details please refer K8S doc