How to Use the Kubernetes NMState Operator to Change the DNS Server IP and Add Options in /etc/resolv.conf on CoreOS Nodes

Environment

• Red Hat OpenShift Container Platform 4.x
• Kubernetes NMState Operator

Issue

• Need to change CoreOS Node DNS server IP
• Need to add options in /etc/resolv.conf

Resolution

• Make sure the Kubernetes NMState Operator is installed.
• Before creating the CR, check the status of node worker-2.ocp4.example.com.

[core@worker-2 ~]$ cat /etc/resolv.conf 
# Generated by NetworkManager
search ocp4.example.com
nameserver 192.168.1.249

• The Operator CR example shown below will change the DNS server IP, search domains, and options on the node worker-2.ocp4.example.com.

$ cat dns-worker2.yaml
apiVersion: nmstate.io/v1
kind: NodeNetworkConfigurationPolicy
metadata:
  name: dns-worker
spec:
  nodeSelector:
    kubernetes.io/hostname: worker-2.ocp4.example.com 
  desiredState:
    dns-resolver:
      config:
        server:
          - 192.168.1.249
          - 192.168.1.1
        search:
          - ocp4.example.com
          - mydomain.com
        options:
          - "rotate"
          - "attempts:3"
          - "timeout:2"

• Then run oc create -f dns-worker2.yaml and check the results on the nodes

[core@worker-2 ~]$ cat /etc/resolv.conf 
# Generated by NetworkManager
search ocp4.example.com mydomain.com
nameserver 192.168.1.249
nameserver 192.168.1.1
options rotate attempts:3 timeout:2

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