一、獲取 yaml 文件

wget https://raw.githubusercontent.com/coredns/deployment/master/kubernetes/coredns.yaml.sed

二、修改文件內(nèi)容

# 主要修改以下 2 處內(nèi)容
  Corefile: |
    .:53 {
        errors
        health
        kubernetes cluster.local 10.0.0.0/24 { 
          pods insecure
          upstream
          fallthrough in-addr.arpa ip6.arpa
        }
        prometheus :9153
        proxy . /etc/resolv.conf
        cache 30
        loop
        reload
        loadbalance
    }

########################################################

# 10.0.0.0/24 是配置文件中 services 網(wǎng)段的地址，參數(shù)如下所示，怎么配置就怎么寫(xiě)
/opt/kubernetes/cfg/kube-apiserver:--service-cluster-ip-range=10.0.0.0/24 \
/opt/kubernetes/cfg/kube-controller-manager:--service-cluster-ip-range=10.0.0.0/24 \
/opt/kubernetes/cfg/kube-proxy:--cluster-cidr=10.0.0.0/24 \

# clusterIP 的值修改為 /opt/kubernetes/cfg/kubelet.config 中配置的 clusterDNS 的值

clusterIP=10.0.0.2

三、部署和測(cè)試

• 部署

kubectl apply -f coredns.yaml

• 測(cè)試成功結(jié)果如下所示

$ dig kubernetes.default.svc.cluster.local @10.0.0.2

; <<>> DiG 9.9.4-RedHat-9.9.4-72.el7 <<>> kubernetes.default.svc.cluster.local @10.0.0.2
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39810
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;kubernetes.default.svc.cluster.local. IN A

;; ANSWER SECTION:
kubernetes.default.svc.cluster.local. 5 IN A    10.0.0.1

;; Query time: 0 msec
;; SERVER: 10.0.0.2#53(10.0.0.2)
;; WHEN: Fri Dec 28 15:49:54 CST 2018
;; MSG SIZE  rcvd: 117

四、遇到的問(wèn)題

• kubernetes 節(jié)點(diǎn)每次重啟后 coredns 失效，此時(shí) ipvsadm 命令顯示結(jié)果如下：

$ ipvsadm
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
TCP  master:https rr
  -> master:sun-sr-https          Masq    1      0          0
TCP  master:domain rr

• crondns pod 的日志顯示如下

E1229 08:48:05.394899       1 reflector.go:205] github.com/coredns/coredns/plugin/kubernetes/controller.go:311: \ 
Failed to list *v1.Service: Get https://10.0.0.1:443/api/v1/services?limit=500&resourceVersion=0 \
: dial tcp 10.0.0.1:443: i/o timeout

• 解決辦法，重啟所有節(jié)點(diǎn)的 kube-proxy 進(jìn)程，刪掉 coredns 并重新創(chuàng)建

# 注意一下命令先后順序
kubectl delete -f coredns.yaml
systemctl restart kube-proxy # 所有節(jié)點(diǎn)
kubectl create -f coredns.yaml

• coredns 正常時(shí) ipvsadm 命令顯示結(jié)果如下

$ ipvsadm
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
TCP  kubernetes.default.svc.clust rr
  -> master:sun-sr-https          Masq    1      0          0
TCP  kube-dns.kube-system.svc.clu rr
  -> 172.18.3.3:domain            Masq    1      0          0

附錄： 完整 coredns.yaml 文件內(nèi)容

$ \cat coredns.yaml
apiVersion: v1
kind: ServiceAccount
metadata:
  name: coredns
  namespace: kube-system
---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRole
metadata:
  labels:
    kubernetes.io/bootstrapping: rbac-defaults
  name: system:coredns
rules:
- apiGroups:
  - ""
  resources:
  - endpoints
  - services
  - pods
  - namespaces
  verbs:
  - list
  - watch
- apiGroups:
  - ""
  resources:
  - nodes
  verbs:
  - get
---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: ClusterRoleBinding
metadata:
  annotations:
    rbac.authorization.kubernetes.io/autoupdate: "true"
  labels:
    kubernetes.io/bootstrapping: rbac-defaults
  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
data:
  Corefile: |
    .:53 {
        errors
        health
        kubernetes cluster.local 10.0.0.0/24 {
          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/name: "CoreDNS"
spec:
  replicas: 2
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxUnavailable: 1
  selector:
    matchLabels:
      k8s-app: kube-dns
  template:
    metadata:
      labels:
        k8s-app: kube-dns
    spec:
      serviceAccountName: coredns
      tolerations:
        - key: "CriticalAddonsOnly"
          operator: "Exists"
      nodeSelector:
        beta.kubernetes.io/os: linux
      containers:
      - name: coredns
        image: coredns/coredns:1.3.0
        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
        securityContext:
          allowPrivilegeEscalation: false
          capabilities:
            add:
            - NET_BIND_SERVICE
            drop:
            - all
          readOnlyRootFilesystem: true
        livenessProbe:
          httpGet:
            path: /health
            port: 8080
            scheme: HTTP
          initialDelaySeconds: 60
          timeoutSeconds: 5
          successThreshold: 1
          failureThreshold: 5
      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"
    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
  - name: metrics
    port: 9153
    protocol: TCP