cat /etc/resolv.conf

nameserver 10.0.0.2

search kube-system.svc.cluster.local svc.cluster.local cluster.local

options ndots:5

[root@VM_0_48_centos coredns]# cat  coredns.yaml

# Warning: This is a file generated from the base underscore template file: coredns.yaml.base

apiVersion: v1

kind: ServiceAccount

metadata:

  name: coredns

  namespace: kube-system

  labels:

      kubernetes.io/cluster-service: "true"

      addonmanager.kubernetes.io/mode: Reconcile

---

apiVersion: rbac.authorization.k8s.io/v1

kind: ClusterRole

metadata:

  labels:

    kubernetes.io/bootstrapping: rbac-defaults

    addonmanager.kubernetes.io/mode: Reconcile

  name: system:coredns

rules:

- apiGroups:

  - ""

  resources:

  - endpoints

  - services

  - pods

  - namespaces

  verbs:

  - list

  - watch

- apiGroups:

  - ""

  resources:

  - nodes

  verbs:

  - get

---

apiVersion: rbac.authorization.k8s.io/v1

kind: ClusterRoleBinding

metadata:

  annotations:

    rbac.authorization.kubernetes.io/autoupdate: "true"

  labels:

    kubernetes.io/bootstrapping: rbac-defaults

    addonmanager.kubernetes.io/mode: EnsureExists

  name: system:coredns

roleRef:

  apiGroup: rbac.authorization.k8s.io

  kind: ClusterRole

  name: system:coredns

subjects:

- kind: ServiceAccount

  name: coredns

  namespace: kube-system

---

apiVersion: v1

kind: ConfigMap

metadata:

  name: coredns

  namespace: kube-system

  labels:

      addonmanager.kubernetes.io/mode: EnsureExists

data:

  Corefile: |

    .:53 {

        errors

        health

        kubernetes cluster.local  in-addr.arpa ip6.arpa {  #cluster.local集群域名

            pods insecure

            upstream

            fallthrough in-addr.arpa ip6.arpa

            ttl 30

        }

        prometheus :9153

        forward . /etc/resolv.conf

        cache 30

        loop

        reload

        loadbalance

    }

---

apiVersion: apps/v1

kind: Deployment

metadata:

  name: coredns

  namespace: kube-system

  labels:

    k8s-app: kube-dns

    kubernetes.io/cluster-service: "true"

    addonmanager.kubernetes.io/mode: Reconcile

    kubernetes.io/name: "CoreDNS"

spec:

  # replicas: not specified here:

  # 1. In order to make Addon Manager do not reconcile this replicas parameter.

  # 2. Default is 1.

  # 3. Will be tuned in real time if DNS horizontal auto-scaling is turned on.

  strategy:

    type: RollingUpdate

    rollingUpdate:

      maxUnavailable: 1

  selector:

    matchLabels:

      k8s-app: kube-dns

  template:

    metadata:

      labels:

        k8s-app: kube-dns

      annotations:

        seccomp.security.alpha.kubernetes.io/pod: 'docker/default'

    spec:

      priorityClassName: system-cluster-critical

      serviceAccountName: coredns

      tolerations:

        - key: "CriticalAddonsOnly"

          operator: "Exists"

      nodeSelector:

        beta.kubernetes.io/os: linux

      containers:

      - name: coredns

        image: k8s.gcr.io/coredns:1.3.1

        imagePullPolicy: IfNotPresent

        resources:

          limits:

            memory: 1024Mi

          requests:

            cpu: 100m

            memory: 70Mi

        args: [ "-conf", "/etc/coredns/Corefile" ]

        volumeMounts:

        - name: config-volume

          mountPath: /etc/coredns

          readOnly: true

        ports:

        - containerPort: 53

          name: dns

          protocol: UDP

        - containerPort: 53

          name: dns-tcp

          protocol: TCP

        - containerPort: 9153

          name: metrics

          protocol: TCP

        livenessProbe:

          httpGet:

            path: /health

            port: 8080

            scheme: HTTP

          initialDelaySeconds: 60

          timeoutSeconds: 5

          successThreshold: 1

          failureThreshold: 5

        readinessProbe:

          httpGet:

            path: /health

            port: 8080

            scheme: HTTP

        securityContext:

          allowPrivilegeEscalation: false

          capabilities:

            add:

            - NET_BIND_SERVICE

            drop:

            - all

          readOnlyRootFilesystem: true

      dnsPolicy: Default

      volumes:

        - name: config-volume

          configMap:

            name: coredns

            items:

            - key: Corefile

              path: Corefile

---

apiVersion: v1

kind: Service

metadata:

  name: kube-dns

  namespace: kube-system

  annotations:

    prometheus.io/port: "9153"

    prometheus.io/scrape: "true"

  labels:

    k8s-app: kube-dns

    kubernetes.io/cluster-service: "true"

    addonmanager.kubernetes.io/mode: Reconcile

    kubernetes.io/name: "CoreDNS"

spec:

  selector:

    k8s-app: kube-dns

  clusterIP: 10.0.0.2   #修改集群的IP

  ports:

  - name: dns

    port: 53

    protocol: UDP

  - name: dns-tcp

    port: 53

    protocol: TCP

  - name: metrics

    port: 9153

    protocol: TCP

[root@VM_0_48_centos coredns]# kubectl  get pods,svc   -n kube-system|grep coredns

pod/coredns-659d5578b7-wg2kp               1/1     Running   0          179m

创建nslookup服务

cat >busybox.yaml<<EOF

apiVersion: v1

kind: Pod

metadata:

  name: busybox

  namespace: default

spec:

  containers:

  - name: busybox

    image: busybox:1.28

    command:

      - sleep

      - "3600"

    imagePullPolicy: IfNotPresent

  restartPolicy: Always

  EOF创建并测试解析kubernetes.default

kubectl create -f busybox.yaml

kubectl get pods busybox

kubectl get pods busybox

kubectl exec busybox -- cat /etc/resolv.conf

kubectl exec -ti busybox -- nslookup kubernetes.default

/alertmanager # nslookup prometheus

Server:    10.0.0.2

Address 1: 10.0.0.2 kube-dns.kube-system.svc.cluster.local

Name:      prometheus

Address 1: 10.0.0.94 prometheus.kube-system.svc.cluster.local