k8s部署coredns自动发现服务

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1、coredns的yaml文件内容如下：

[root@k8s_master ~]# cat 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
data:
  Corefile: |
    .:53 {
        errors
        log
        health
        kubernetes cluster.local 10.254.0.0/18      #根据kubelet的配置文件修改此处信息
        proxy . /etc/resolv.conf
        cache 30
    }
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: coredns
  namespace: kube-system
  labels:
    k8s-app: coredns
    kubernetes.io/cluster-service: "true"
    kubernetes.io/name: "CoreDNS"
spec:
  replicas: 1
  selector:
    matchLabels:
      k8s-app: coredns
  template:
    metadata:
      labels:
        k8s-app: coredns
      annotations:
        scheduler.alpha.kubernetes.io/critical-pod: ''
        scheduler.alpha.kubernetes.io/tolerations: '[{"key":"CriticalAddonsOnly", "operator":"Exists"}]'
    spec:
      serviceAccountName: coredns
      containers:
      - name: coredns
        image: jicki/coredns:latest
        imagePullPolicy: Always
        args: [ "-conf", "/etc/coredns/Corefile" ]
        volumeMounts:
        - name: config-volume
          mountPath: /etc/coredns
        ports:
        - containerPort: 53
          name: dns
          protocol: UDP
        - containerPort: 53
          name: dns-tcp
          protocol: TCP
        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: coredns
  namespace: kube-system
  labels:
    k8s-app: coredns
    kubernetes.io/cluster-service: "true"
    kubernetes.io/name: "CoreDNS"
spec:
  selector:
    k8s-app: coredns
  clusterIP: 10.254.0.2
  ports:
  - name: dns
    port: 53
    protocol: UDP
  - name: dns-tcp
    port: 53
    protocol: TCP

2、创建coredns

kubectl create -f coredns.yaml

3、检查服务是否启动成功

[root@k8s_master ~]# kubectl get pod --all-namespaces
NAMESPACE     NAME                                          READY   STATUS    RESTARTS   AGE
kube-system   coredns-67cb7b5f46-9lmrd                      1/1     Running   0          17h

[root@k8s_master ~]# kubectl get svc --all-namespaces
NAMESPACE     NAME                   TYPE        CLUSTER-IP       EXTERNAL-IP     PORT(S)             AGE
kube-system   coredns                ClusterIP   10.254.0.2       <none>          53/UDP,53/TCP       17h

4、验证是否可用

[root@k8s_master ~]# kubectl exec -it mytomcat-6fddd8f74b-vj8s5  -- ping nginx
PING nginx.default.svc.cluster.local (10.254.60.19) 56(84) bytes of data

[root@k8s_master ~]# kubectl exec -it mytomcat-6fddd8f74b-vj8s5 bash
root@mytomcat-6fddd8f74b-vj8s5:/usr/local/tomcat# curl -I nginx:88
HTTP/1.1 200 OK
Server: nginx/1.15.8
Date: Sat, 29 Dec 2018 07:17:32 GMT
Content-Type: text/html
Content-Length: 612
Last-Modified: Tue, 25 Dec 2018 09:56:47 GMT
Connection: keep-alive
ETag: "5c21fedf-264"
Accept-Ranges: bytes
说明：出现以上说明成功解析

说明：croedns在k8s的1.8和1.12版本已验证没有问题，可以完美部署

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