10 安装coredns

coredns部署(服务发现插件)
服务发现就是服务（应用）之间相互定位的过程
服务发现并非云计算时代独有的，传统的单体架构也有
服务(应用)的动态性强
服务(应用)更新发布频繁
服务(应用)支持自动伸缩

在K8S集群里，pod的ip是不断变化的，如何以不变应万变
    抽象出了service资源，通过标签选择器，关联一组pod
    抽象出了集群网络，通过相对固定的 “集群IP”，使服务接入点固
自动关联service资源的 “名称” 和 “集群网络IP”，从而达到服务被集群自动发现的目的

部署K8S的内网资源配置清单http服务
rstx-53上：
vim /etc/nginx/conf.d/k8s-yaml.rongbiz.cn.conf

server {
    listen       80;
    server_name  k8s-yaml.rongbiz.cn;

    location / {
        autoindex on;
        default_type text/plain;
        root /data/k8s-yaml;
    }
}

nginx -s reload

k8s-yaml     A      192.168.1.53

mkdir -p /data/k8s-yaml

docker pull coredns/coredns:1.7.0

docker tag bfe3a36ebd25 harbor.rongbiz.cn/public/coredns:v1.7.0
docker push harbor.rongbiz.cn/public/coredns:v1.7.0 

mkdir /data/k8s-yaml/coredns -p

创建coredns配置文件
定义集群角色

cat rbac.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

创建配置文件

cat cm.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: coredns
  namespace: kube-system
data:
  Corefile: |
    .:53 {
        errors
        log
        health
        ready
        kubernetes cluster.local 10.254.0.0/16
        forward . 192.168.1.201
        cache 30
        loop
        reload
        loadbalance
       }

创建pod控制器

cat dp.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: coredns
  namespace: kube-system
  labels:
    k8s-app: coredns
    kubernetes.io/name: "CoreDNS"
spec:
  replicas: 1
  selector:
    matchLabels:
      k8s-app: coredns
  template:
    metadata:
      labels:
        k8s-app: coredns
    spec:
      priorityClassName: system-cluster-critical
      serviceAccountName: coredns
      containers:
      - name: coredns
        image: harbor.rongbiz.cn/public/coredns:v1.7.0
        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
        - containerPort: 9153
          name: metrics
          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

创建svc资源
cat svc.yaml

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
  - name: metrics
    port: 9153
    protocol: TCP

部署coredns

kubectl apply -f http://k8s-yaml.rongbiz.cn/coredns/rbac.yaml
kubectl apply -f http://k8s-yaml.rongbiz.cn/coredns/cm.yaml
kubectl apply -f http://k8s-yaml.rongbiz.cn/coredns/dp.yaml
kubectl apply -f http://k8s-yaml.rongbiz.cn/coredns/svc.yaml

验证

dig -t A kubernetes.default.svc.cluster.local. @10.254.0.2 +short
10.254.0.1