K8S 之 Coredns安装与理解

一、Coredns作用

重点：通过coredns 通过service名称，解释到相应的cluter集群IP

二、Coredns安装(以容器搭建服务)

1、在运维主机上搭建一个HTTP服务存放yaml文件

~]# cd /etc/nginx/conf.d/conf.d]# vi /etc/nginx/conf.d/k8s-yaml.od.com.confserver {    listen       80;    server_name  k8s-yaml.od.com;    location / {        autoindex on;        default_type text/plain;        root /data/k8s-yaml;    }}conf.d]# mkdir /data/k8s-yamlconf.d]# nginx -tconf.d]# nginx -s reloadconf.d]# cd /data/k8s-yaml/k8s-yaml]# mkdir coredns

2、创建四个yaml文件，用于coredns容器创建

[root@test-operator coredns]# cat rbac.yaml apiVersion: v1kind: ServiceAccountmetadata:  name: coredns  namespace: kube-system  labels:      kubernetes.io/cluster-service: "true"      addonmanager.kubernetes.io/mode: Reconcile---apiVersion: rbac.authorization.k8s.io/v1kind: ClusterRolemetadata:  labels:    kubernetes.io/bootstrapping: rbac-defaults    addonmanager.kubernetes.io/mode: Reconcile  name: system:corednsrules:- apiGroups:  - ""  resources:  - endpoints  - services  - pods  - namespaces  verbs:  - list  - watch---apiVersion: rbac.authorization.k8s.io/v1kind: ClusterRoleBindingmetadata:  annotations:    rbac.authorization.kubernetes.io/autoupdate: "true"  labels:    kubernetes.io/bootstrapping: rbac-defaults    addonmanager.kubernetes.io/mode: EnsureExists  name: system:corednsroleRef:  apiGroup: rbac.authorization.k8s.io  kind: ClusterRole  name: system:corednssubjects:- kind: ServiceAccount  name: coredns  namespace: kube-system-----------------------------------------------------------------------------------------------[root@test-operator coredns]# cat cm.yamlapiVersion: v1kind: ConfigMapmetadata:  name: coredns  namespace: kube-systemdata:  Corefile: |    .:53 {        errors        log        health        ready        kubernetes cluster.local 192.168.0.0/16        forward . 10.3.151.13        cache 30        loop        reload        loadbalance       }-----------------------------------------------------------------------------------------------[root@test-operator coredns]# cat dp.yamlapiVersion: apps/v1kind: Deploymentmetadata:  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: test-harbor.cedarhd.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-----------------------------------------------------------------------------------------------[root@test-operator coredns]# cat svc.yaml apiVersion: v1kind: Servicemetadata:  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、在其中一个节点服务器运行coredns(安装成功)

[root@test-nodes1 ~]# kubectl apply -f http://k8s-yaml.cedarhd.com/coredns/rbac.yamlserviceaccount/coredns createdclusterrole.rbac.authorization.k8s.io/system:coredns createdclusterrolebinding.rbac.authorization.k8s.io/system:coredns created[root@test-nodes1 ~]# kubectl apply -f http://k8s-yaml.cedarhd.com/coredns/cm.yamlconfigmap/coredns created[root@test-nodes1 ~]# kubectl apply -f http://k8s-yaml.cedarhd.com/coredns/dp.yamldeployment.apps/coredns created[root@test-nodes1 ~]# kubectl apply -f http://k8s-yaml.cedarhd.com/coredns/svc.yamlservice/coredns created[root@test-nodes1 ~]# kubectl get all -n kube-systemNAME                           READY   STATUS    RESTARTS   AGEpod/coredns-6c69fbcc6c-6vqgr   1/1     Running   0          35sNAME              TYPE        CLUSTER-IP    EXTERNAL-IP   PORT(S)                  AGEservice/coredns   ClusterIP   192.168.0.2           53/UDP,53/TCP,9153/TCP   14sNAME                      READY   UP-TO-DATE   AVAILABLE   AGEdeployment.apps/coredns   1/1     1            1           36sNAME                                 DESIRED   CURRENT   READY   AGEreplicaset.apps/coredns-6c69fbcc6c   1         1         1       36s

三、使用场景描述

1、创建一个新的svc资源[root@test-nodes1 ~]# kubectl create deployment nginx-test --image=test-harbor.cedarhd.com/public/nginx:v1.7.9deployment.apps/nginx-test created[root@test-nodes1 ~]# kubectl get all NAME                              READY   STATUS    RESTARTS   AGEpod/nginx-test-5674474869-c4mzx   1/1     Running   0          5sNAME                 TYPE        CLUSTER-IP    EXTERNAL-IP   PORT(S)   AGEservice/kubernetes   ClusterIP   192.168.0.1           443/TCP   8hNAME                         READY   UP-TO-DATE   AVAILABLE   AGEdeployment.apps/nginx-test   1/1     1            1           5sNAME                                    DESIRED   CURRENT   READY   AGEreplicaset.apps/nginx-test-5674474869   1         1         1       5s[root@test-nodes1 ~]# kubectl expose deployment nginx-test --port=80service/nginx-test exposed[root@test-nodes1 ~]# kubectl get allNAME                              READY   STATUS    RESTARTS   AGEpod/nginx-test-5674474869-c4mzx   1/1     Running   0          42sNAME                 TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)   AGEservice/kubernetes   ClusterIP   192.168.0.1              443/TCP   8hservice/nginx-test   ClusterIP   192.168.109.13           80/TCP    8s  #创建svc为nginx-test 对应的cluterip为192.168.109.13NAME                         READY   UP-TO-DATE   AVAILABLE   AGEdeployment.apps/nginx-test   1/1     1            1           42sNAME                                    DESIRED   CURRENT   READY   AGEreplicaset.apps/nginx-test-5674474869   1         1         1       42s2、进入其中一个容器查看解释效果[root@test-nodes2 ~]# kubectl get pods -n kube-publicNAME             READY   STATUS    RESTARTS   AGEnginx-ds-dk9hf   1/1     Running   0          3h53mnginx-ds-m6v9q   1/1     Running   0          3h53m[root@test-nodes2 ~]# kubectl exec -ti nginx-ds-dk9hf /bin/bash -n kube-publicPING nginx-test.default.svc.cluster.local (192.168.109.13) 56(84) bytes of data.64 bytes from nginx-test.default.svc.cluster.local (192.168.109.13): icmp_seq=1 ttl=64 time=0.070 ms64 bytes from nginx-test.default.svc.cluster.local (192.168.109.13): icmp_seq=2 ttl=64 time=0.077 ms#nginx-test.default       defalut(容器所在的空间，必须加)