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.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
conf.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: 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
-----------------------------------------------------------------------------------------------

[root@test-operator coredns]# cat 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 . 10.3.151.13
        cache 30
        loop
        reload
        loadbalance
       }
-----------------------------------------------------------------------------------------------

[root@test-operator coredns]# cat 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: 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: 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、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.yaml
serviceaccount/coredns created
clusterrole.rbac.authorization.k8s.io/system:coredns created
clusterrolebinding.rbac.authorization.k8s.io/system:coredns created
[root@test-nodes1 ~]# kubectl apply -f http://k8s-yaml.cedarhd.com/coredns/cm.yaml
configmap/coredns created
[root@test-nodes1 ~]# kubectl apply -f http://k8s-yaml.cedarhd.com/coredns/dp.yaml
deployment.apps/coredns created
[root@test-nodes1 ~]# kubectl apply -f http://k8s-yaml.cedarhd.com/coredns/svc.yaml
service/coredns created
[root@test-nodes1 ~]# kubectl get all -n kube-system
NAME                           READY   STATUS    RESTARTS   AGE
pod/coredns-6c69fbcc6c-6vqgr   1/1     Running   0          35s
NAME              TYPE        CLUSTER-IP    EXTERNAL-IP   PORT(S)                  AGE
service/coredns   ClusterIP   192.168.0.2   <none>        53/UDP,53/TCP,9153/TCP   14s
NAME                      READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/coredns   1/1     1            1           36s
NAME                                 DESIRED   CURRENT   READY   AGE
replicaset.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:v1.7.9
deployment.apps/nginx-test created
[root@test-nodes1 ~]# kubectl get all 
NAME                              READY   STATUS    RESTARTS   AGE
pod/nginx-test-5674474869-c4mzx   1/1     Running   0          5s
NAME                 TYPE        CLUSTER-IP    EXTERNAL-IP   PORT(S)   AGE
service/kubernetes   ClusterIP   192.168.0.1   <none>        443/TCP   8h
NAME                         READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/nginx-test   1/1     1            1           5s
NAME                                    DESIRED   CURRENT   READY   AGE
replicaset.apps/nginx-test-5674474869   1         1         1       5s

[root@test-nodes1 ~]# kubectl expose deployment nginx-test --port=80
service/nginx-test exposed
[root@test-nodes1 ~]# kubectl get all
NAME                              READY   STATUS    RESTARTS   AGE
pod/nginx-test-5674474869-c4mzx   1/1     Running   0          42s
NAME                 TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)   AGE
service/kubernetes   ClusterIP   192.168.0.1      <none>        443/TCP   8h
service/nginx-test   ClusterIP   192.168.109.13   <none>        80/TCP    8s  
#创建svc为nginx-test 对应的cluterip为192.168.109.13
NAME                         READY   UP-TO-DATE   AVAILABLE   AGE
deployment.apps/nginx-test   1/1     1            1           42s
NAME                                    DESIRED   CURRENT   READY   AGE
replicaset.apps/nginx-test-5674474869   1         1         1       42s

2、进入其中一个容器查看解释效果
[root@test-nodes2 ~]# kubectl get pods -n kube-public
NAME             READY   STATUS    RESTARTS   AGE
nginx-ds-dk9hf   1/1     Running   0          3h53m
nginx-ds-m6v9q   1/1     Running   0          3h53m
[root@test-nodes2 ~]# kubectl exec -ti nginx-ds-dk9hf /bin/bash -n kube-public
PING 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 ms
64 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)