安装部署coredns（服务发现）_基于 Kubernetes 的 PaaS

WHAT ：服务（应用）之间相互定位的过程

WHY：

服务发现对应的场景：

服务（应用）的动态性抢

服务（应用）更新发布频繁

服务（应用）支持自动伸缩

kuberntes中的所有pod都是基于Service域名解析后，再负载均衡分发到service后端的各个pod服务中，POD的IP是不断变化的。如何解决：

抽象出Service资源，通过标签选择器，关联一组POD

抽象出集群网络，通过固定的“集群IP”，使服务接入点固定

如何管理Service资源的“名称”和“集群网络IP”

我们前面做了传统的DNS模型：hdss7-21.host.com -> 10.4.7.21

那么我们可以在K8S里做这样的模型：nginx-ds -> 192.168.0.1

# 现在我们要开始用交付容器方式交付服务（非二进制），这也是以后最常用的方式
# 200机器
certs]# cd /etc/nginx/conf.d/
conf.d]# vi /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;
    }
}
conf.d]# mkdir /data/k8s-yaml
conf.d]# nginx -t
conf.d]# nginx -s reload

# 11机器，解析域名：
~]# vi /var/named/od.com.zone
serial 前滚一位
# 最下面添加这个网段，以后也都是在最下面添加，后面我就加这个注释了
k8s-yaml           A    10.4.7.200
~]# systemctl restart named
~]# dig -t A k8s-yaml.od.com @10.4.7.11 +short
# out：10.4.7.200

dig -t A ：指的是找DNS里标记为A的相关记录，@用什么机器IP访问，+short是只返回IP

# 200机器
conf.d]# cd /data/k8s-yaml/
k8s-yaml]# mkdir coredns

# 200机器，下载coredns镜像：
cd /data/k8s-yaml/
k8s-yaml]# docker pull coredns/coredns:1.6.1
k8s-yaml]# docker images|grep coredns
k8s-yaml]# docker tag c0f6e815079e harbor.od.com/public/coredns:v1.6.1
k8s-yaml]# docker push !$

这里我们需要注意的是，任何我用到的镜像都会推到我的本地私有仓库，原因前面也说了，1、是为了用的时候速度快保证不出现网络问题，2、保证版本是同样的版本，而不是突然被别人修改了

docker push !$ ：push上一个镜像的名字

# 200机器，准备资源配置清单：
cd /data/k8s-yaml/coredns
coredns]# vi 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
  
coredns]# vi cm.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: coredns
  namespace: kube-system
data:
  Corefile: |
    .:53 {
        errors
        log
        health
        ready
        kubernetes cluster.local 192.168.0.0/16
        forward . 10.4.7.11
        cache 30
        loop
        reload
        loadbalance
       }
   
coredns]# vi 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
    
coredns]# vi 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

# 21机器，应用资源配置清单（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
~]# kubectl get all -n kube-system

CLUSTER-IP为什么是192.168.0.2 ：因为我们之前已经写死了这是我们dns的统一接入点

# 21机器，测试（我的已经存在了，不过不影响）：
~]# kubectl create deployment nginx-dp --image=harbor.od.com/public/nginx:v1.7.9 -n kube-public
~]# kubectl expose deployment nginx-dp --port=80 -n kube-public
~]# kubectl get svc -n kube-public
~]# dig -t A nginx-dp.kube-public.svc.cluster.local. @192.168.0.2 +short
# out：192.168.81.37

dig -t A ：指的是找DNS里标记为A的相关记录，@用什么机器IP访问，+short是只返回IP