K8S入门系列之必备扩展组件--> coredns(四)

摘要：

• 集群其他组件全部完成后我们应当部署集群 DNS 使 service 等能够正常解析，1.11版本coredns已经取代kube-dns成为集群默认dns。
• https://github.com/coredns/deployment/blob/master/kubernetes/

1. yaml配置清单

[root@k8s-master01 ~]# mkdir -p /opt/coredns
[root@k8s-master01 ~]# vi /opt/coredns/coredns.yaml

apiVersion: v1
kind: ServiceAccount
metadata:
  name: coredns
  namespace: kube-system
---
apiVersion: rbac.authorization.k8s.io/v1
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/v1
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 {
          lameduck 5s
        }
        ready
        kubernetes cluster.local 10.96.0.0/16 {    # 修改 clusterIP等
          pods insecure
          fallthrough in-addr.arpa ip6.arpa
        }FEDERATIONS
        prometheus :9153
        forward . /etc/resolv.conf    # 需要调用环境变量/etc/resolv.conf
        cache 30
        loop
        reload
        loadbalance
    }
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: coredns
  namespace: kube-system
  labels:
    k8s-app: kube-dns
    kubernetes.io/name: "CoreDNS"
spec:
  # replicas: not specified here:
  # 1. Default is 1.
  # 2. 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
    spec:
      priorityClassName: system-cluster-critical
      serviceAccountName: coredns
      tolerations:
        - key: "CriticalAddonsOnly"
          operator: "Exists"
      nodeSelector:
        beta.kubernetes.io/os: linux
      affinity:
        podAntiAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
          - labelSelector:
              matchExpressions:
              - key: k8s-app
                operator: In
                values: ["kube-dns"]
            topologyKey: kubernetes.io/hostname
      containers:
      - name: coredns
        image: coredns/coredns:1.6.5    # 镜像仓库地址, 不可用可更换!
        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
        readinessProbe:
          httpGet:
            path: /ready
            port: 8181
            scheme: HTTP
      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: 10.96.0.2    # 设置cluster_DNS_IP
  ports:
  - name: dns
    port: 53
    protocol: UDP
  - name: dns-tcp
    port: 53
    protocol: TCP
  - name: metrics
    port: 9153
    protocol: TCP

参数解释：

　　1）errors官方没有明确解释，后面研究

　　2）health:健康检查，提供了指定端口（默认为8080）上的HTTP端点，如果实例是健康的，则返回“OK”。

　　3）cluster.local：CoreDNS为kubernetes提供的域，10.96.0.0/16这告诉Kubernetes中间件它负责为反向区域提供PTR请求0.0.96.10.in-addr.arpa ..换句话说，这是允许反向DNS解析服务（我们经常使用到得DNS服务器里面有两个区域，即“正向查找区域”和“反向查找区域”，正向查找区域就是我们通常所说的域名解析，反向查找区域即是这里所说的IP反向解析，它的作用就是通过查询IP地址的PTR记录来得到该IP地址指向的域名，当然，要成功得到域名就必需要有该IP地址的PTR记录。PTR记录是邮件交换记录的一种，邮件交换记录中有A记录和PTR记录，A记录解析名字到地址，而PTR记录解析地址到名字。地址是指一个客户端的IP地址，名字是指一个客户的完全合格域名。通过对PTR记录的查询，达到反查的目的。）

　　4）proxy:这可以配置多个upstream 域名服务器，也可以用于延迟查找 /etc/resolv.conf 中定义的域名服务器

　　5）cache:这允许缓存两个响应结果，一个是肯定结果（即，查询返回一个结果）和否定结果（查询返回“没有这样的域”），具有单独的高速缓存大小和TTLs。

　　# 这里 kubernetes cluster.local 为创建 svc 的 IP 段

　　kubernetes cluster.local 10.96.0.0/16

　　# clusterIP 为指定 DNS 的 IP

2. 创建

[root@k8s-master01 ~]# kubectl apply -f /opt/coredns/coredns.yaml