Centos7 k8s v1.5.2二进制部署安装-服务发现

一、服务发现

　　1、概念

　　　　简单来说，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，传统的单体架构时代也会用到。以下应用场景下，更需要服务发现
　　　　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”，使服务接入点固定
　　　　那么如何自动关联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呢？
　　　　考虑传统DNS的模型：hdss7-21.host.com->10.4.7.21
　　　　能否在k8s里建立这样的模型：nginx-ds->192.168.0.5
　　2、k8s里服务发现的方式-DNS
　　3、实现k8s里DNS功能的插件（软件）
　　　　kube-dns-kubernetes-v1.2至kubernetes-v1.10
　　　　Coredns-kubernetes-v1.11至今
　　注意：k8s里的DNS不是万能的！它应该只负责自动维护“服务名”->"集群网络IP"之间的关系

二、部署k8s的核心组件（CoreDNS）

　　1、编写配置文件

vim /etc/nginx/conf.d/k8s-yaml.od.com.conf
server {
      listen        80;
      server_name   k8s-yaml.od.com;

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

　　2、创建yaml文件

vim /data/k8s-yaml/coredns/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
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: coredns
  namespace: kube-system
data:
  Corefile: |
    .:53 {
        errors
        log
        health
        kubernetes cluster.local 182.168.0.0/16      #鏍规嵁kubelet鐨勯厤缃�枃浠朵慨鏀规�澶勪俊鎭�
        forward . 192.168.112.60
        cache 30
        loop
        reload
        loadbalance
    }

vim /data/k8s-yaml/coredns/cm.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: coredns
  namespace: kube-system
data:
  Corefile: |
    .:53 {
        errors
        log
        health
        kubernetes cluster.local 192.168.0.0/16      #鏍规嵁kubelet鐨勯厤缃�枃浠朵慨鏀规�澶勪俊鎭�
        forward  . 192.168.112.60
        cache 30
    }

vim /data/k8s-yaml/coredns/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.od.com/public/coredns:v1.6.1
        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

vim /data/k8s-yaml/coredns/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: 192.168.0.2
  ports:
  - name: dns
    port: 53
    protocol: UDP
  - name: dns-tcp
    port: 53
  - name: metrics
    port: 9153
    protocol: TCP

　　3、修改dns

[root@slave1 ~]# vim /var/named/od.com.zone
k8s-yaml A 192.168.112.24

systemctl restart named

　　4、docker下载镜像

docker pull docker.io/coredns/coredns:1.6.1
docker tag c0f6e815079e harbor.od.com/public/coredns:v1.6.1
docker push harbor.od.com/public/coredns:v1.6.1

　　5、用陈述式

kubectl apply -f http://k8s-yaml.od.com/coredns/rbac.yaml
kubectl apply -f http://k8s-yaml.od.com/coredns/cm.yaml
kubectl apply -f http://k8s-yaml.od.com/coredns/dp.yaml
kubectl apply -f http://k8s-yaml.od.com/coredns/svc.yaml

 　　6、测试

dig -t A k8s-yaml.bbdops.com @192.168.0.2 +short
10.61.10.43dig -t A www.baidu.com  @192.168.0.2 +short
www.a.shifen.com.
110.242.68.dig -t A k8s-yaml.bbdops.com @192.168.0.2 +short
10.61.10.43