一、構建coredns服務

將下載的 kubernetes-server-linux-amd64.tar.gz 解壓後，再解壓其中的 kubernetes-src.tar.gz 檔案。coredns 對應的目錄是：cluster/addons/dns。

cd /opt/test/kubernetes/cluster/addons/dns/coredns

將coredns模板複製出來：

cp coredns.yaml.base /opt/yml_files/coredns.yaml

修改一些引數：
修改引數有3個地方，一個是ip6.arpa 指定，一個是更改成國內映象源，一個是定義clusterIP，具體如下

[[email protected]
 
 coredns]# diff coredns.yaml.base /opt/yml_files/coredns.yaml
61c61
<         kubernetes __PILLAR__DNS__DOMAIN__ in-addr.arpa ip6.arpa {
---
>         kubernetes cluster.local. in-addr.arpa ip6.arpa {
111c111
<         image: k8s.gcr.io/coredns:1.2.2
---
>         image: registry.cn-hangzhou.aliyuncs.com/google_containers/coredns:1.2.6
176c176
<   clusterIP: __PILLAR__DNS__SERVER__
---
>   clusterIP: 10.0.0.2
 

完整的yaml檔案：

[[email protected] yml_files]# cat coredns.yaml
# __MACHINE_GENERATED_WARNING__

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: registry.cn-hangzhou.aliyuncs.com/google_containers/coredns:1.2.6
        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
 

建立dns:

kubectl create -f coredns.yaml

檢測：

kubectl get all -n kube-system

二、測試：

建立一個簡單的centos,busybox有點坑，測試有問題。
.

[[email protected] yml_files]# cat centos.yaml
apiVersion: v1
kind: Pod
metadata:
  name: centoschao
  namespace: default
spec:
  containers:
  - image: centos
    command:
      - sleep
      - "3600"
    imagePullPolicy: IfNotPresent
    name: centoschao
  restartPolicy: Always

建立：

kubectl create -f centos.yaml

驗證

kubectl exec -it centoschao sh
yum install bind-utils -y

然後退出來：

[[email protected] yml_files]#  kubectl exec -ti centoschao -- nslookup kubernetes.default
Server:		10.0.0.2
Address:	10.0.0.2#53

Name:	kubernetes.default.svc.cluster.local
Address: 10.0.0.1

此處 dns部署成功