CoreDNS: k8s内部的DNS ,用于对pod对service做记录的，好让其他的pod做访问

这里不用做过多的阐述

官方kube-dns现在已经没有在维护了，从Kubernetes 1.11开始，可使用CoreDNS作为Kubernetes的DNS插件进入GA状态，Kubernetes推荐使用CoreDNS作为集群内的DNS服务。 CoreDNS从2017年初就成为了CNCF的的孵化项目，CoreDNS的特点就是十分灵活和可扩展的插件机制，各种插件实现

vim coredns.yaml

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

---

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 {

            pods insecure

            upstream

            fallthrough in-addr.arpa ip6.arpa

        }

        prometheus :9153

        proxy . /etc/resolv.conf

        cache 30

        loop

        reload

        loadbalance

    }

---

apiVersion: extensions/v1beta1

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:

      serviceAccountName: coredns

      tolerations:

        - key: node-role.kubernetes.io/master

          effect: NoSchedule

        - key: "CriticalAddonsOnly"

          operator: "Exists"

      containers:

      - name: coredns

        image: coredns/coredns:1.2.2

        imagePullPolicy: IfNotPresent

        resources:

          limits:

            memory: 170Mi

          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

        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

  ports:

  - name: dns

    port: 53

    protocol: UDP

  - name: dns-tcp

    port: 53

    protocol: TCP

创建coredns

 [root@k8s-master ~]# kubectl create -f coredns.yaml

[root@k8s-master ~]# kubectl get pod,svc,deployment,rc -n kube-system

NAME                           READY   STATUS    RESTARTS   AGE

pod/coredns-5d7754fbcb-hm6vq   1/1     Running   0          3m36s

NAME               TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)         AGE

service/kube-dns   ClusterIP   10.0.0.2             53/UDP,53/TCP   97s

NAME                            READY   UP-TO-DATE   AVAILABLE   AGE

deployment.extensions/coredns   1/1     1            1           3m36s