### k8s的服务发现插件---CoreDNS 服务发现需要解决的问题： 　　1、服务动态性强--容器在k8s中ip变化或迁移 　　2、更新发布频繁--版本迭代快 　　3、支持自动伸缩--大促或流量高峰 我们为了解决pod地址变化的问题，我们之前部署了service资源，将pod地址通过service资源暴露的固定地址，来解决以上问题，那么，如何解决service资源名称和service资源暴露出来的集群网络IP做自动的对应呢，从而达到服务的自动发现呢？ 在k8s中，coredns就是为了解决以上问题。 从coredns开始，我们采用向k8s中交付容器的方式，来部署服务，并且使用声明式的方式，来部署服务。 1、部署k8s的内网资源配置清单http服务 运维主机上，配置一个nginx虚拟主机，用以提供k8s统一的资源配置清单访问入口 ``` cat /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; } } ``` #### 加载nginx ``` nginx -t nginx -s reload ``` #### bind9添加A记录 ``` vi /var/named/od.com.zone k8s-yaml A 10.4.7.200 systemctl restart named dig -t A k8s-yaml.od.com @10.4.7.11 +short 10.4.7.200 mkdir -p /data/k8s-yaml/coredns cd /data/k8s-yaml/coredns ``` #### 部署coredns 准备镜像 ``` docker pull 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 ``` #### 准备资源配置清单 官方地址：https://github.com/kubernetes/kubernetes/blob/master/cluster/addons/dns/coredns/coredns.yaml.base 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 ``` 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 #service资源cluster地址 forward . 10.4.7.11 #上级DNS地址 cache 30 loop reload loadbalance } ``` 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 ``` 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 ``` #### 创建查看 ``` 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 [root@hdss7-21 ~]# kubectl get all -n kube-system NAME READY STATUS RESTARTS AGE pod/coredns-594f5bd7bb-24d5b 1/1 Running 0 45s NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE service/coredns ClusterIP 192.168.0.2 <none> 53/UDP,53/TCP,9153/TCP 39s NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE deployment.apps/coredns 1 1 1 1 45s NAME DESIRED CURRENT READY AGE replicaset.apps/coredns-594f5bd7bb 1 1 1 45s ``` #### 验证k8s-dns ``` [root@hdss7-21 ~]# dig -t A www.baidu.com @192.168.0.2 +short www.a.shifen.com. 180.101.49.12 180.101.49.11 ```