Check connection to openshift coredns endpoints

dns-checker.daemonset.yaml

# How to deploy:
# oc new-project dns-checker
# oc adm policy add-cluster-role-to-user cluster-reader -z default
# oc apply -f ...
# Example logout: 
#   # Collected DNS Endpoints: 10.129.0.40 10.129.2.5 10.130.0.13 10.130.2.3 10.131.0.7 10.131.2.3
#   # Run on Node: compute-1.ocp3.stormshift.coe.muc.redhat.com
#   # Fri Jan  8 13:04:32 UTC 2021
#   DNS IP: 10.129.0.40      : PASS      (Details: 172.30.0.1 from server 10.129.0.40 in 0 ms. )
#   DNS IP: 10.129.2.5       : PASS      (Details: 172.30.0.1 from server 10.129.2.5 in 0 ms. )
#   DNS IP: 10.130.0.13      : PASS      (Details: 172.30.0.1 from server 10.130.0.13 in 3 ms. )
#   DNS IP: 10.130.2.3       : PASS      (Details: 172.30.0.1 from server 10.130.2.3 in 1 ms. )
#   DNS IP: 10.131.0.7       : PASS      (Details: 172.30.0.1 from server 10.131.0.7 in 0 ms. )
#   DNS IP: 10.131.2.3       : PASS      (Details: 172.30.0.1 from server 10.131.2.3 in 0 ms. )

apiVersion: apps/v1
kind: DaemonSet
metadata:
  creationTimestamp: null
  labels:
    run: dns-checker
  name: dns-checker
spec:
  updateStrategy:
    type: OnDelete
  selector:
    matchLabels:
      run: dns-checker
  template:
    metadata:
      creationTimestamp: null
      labels:
        run: dns-checker
    spec:
      tolerations:
      - operator: Exists
      containers:
      - image: quay.io/openshift-examples/toolbox:main
        imagePullPolicy: Always
        name: dns-checker
        command:
          - /bin/bash
          - -c
          - |
            #!/bin/bash
            while true; do
              DNS_ENDPOINTS=$( curl --silent \
                --cacert /run/secrets/kubernetes.io/serviceaccount/ca.crt \
                --header "Authorization: Bearer $(cat /run/secrets/kubernetes.io/serviceaccount/token)" \
                https://kubernetes.default.svc.cluster.local/api/v1/namespaces/openshift-dns/endpoints/dns-default | jq '.subsets[] | .addresses[] | .ip' -r | tr "\n " " ")
              echo "# Collected DNS Endpoints: $DNS_ENDPOINTS"
              echo "# Run on Node: $K8S_NODENAME"
              echo -n "# ";date
              for i in $DNS_ENDPOINTS ; do
                printf "DNS IP: %-16s : " $i
                RESULT=$(dig -p 5353 +retry=1 +tries=1 +time=1 +short +identify  kubernetes.default.svc.cluster.local. @${i})
                RC=$?
                if [ $RC -gt 0 ] ; then
                  echo -n "FAIL (RC: $RC)"
                else
                  echo -n "PASS"
                fi
                echo -n "      (Details: $RESULT )"
                echo ""
              done
              sleep 5;
            done;
        env:
        - name: K8S_NODENAME
          valueFrom:
            fieldRef:
              fieldPath: spec.nodeName