1) Core-dns pod instability issue - CrashloopBack off / Error / Restarts while executing

$ kubectl get pods -n kube-system

Cause: /etc/resolv.conf is not configured properly to establish the network with coredns pod.

Solution:

check /etc/resolv.conf  → whether it is having the content as below

nameserver 8.8.8.8

2) Calico pods ( CNI ) instability issue - restarting the calico pods with unstable network connectivity

while executing $ kubectl get pods -n kube-system or getting BGP connection not estabilished in calico-node-<xyz> . Bird is not ready

while executing $ kubectl describe pods -n  kube-system calico-node-<xyz>

Cause: Error occurred due to network interface of the vm / machine which calico cni is using can't be able to connect to the internet.

Solution:

We have to execute below command in ELIOT Master node

$ kubectl set env daemonset/calico-node -n kube-system IP_AUTODETECTION_METHOD=can-reach=www.google.com    

                                                                                                          ( or )

$ kubectl set env daemonset/calico-node -n kube-system IP_AUTODETECTION_METHOD=interface=<interface-name>

<interface-name> must be the interface which the machine / VM can be able to connect with the internet

Kindly refer the below link to check detailed info

https://docs.projectcalico.org/networking/ip-autodetection