15-DNS的解析策略

一、默认的解析策略ClusterFirst

1.作用

​ ClusterFirst，表示以集群的DNS解析优先，特指的是我们的CoreDNS服务，运行的容器内，DNS解析文件默认指向的是kube-dns即集群的，默认DNS服务

2.测试

[root@master231 deployments]# cat 05-deploy-dnsPolicy.yaml 
apiVersion: apps/v1
kind: Deployment
metadata:
  name: deploy-xiuxian-dnspolicy
  labels:
    apps: xiuxian
spec:
  replicas: 5
  selector:
    matchLabels:
      version: v1
  template:
    metadata:
      labels:
        version: v1
        school: oldboyedu
        class: linux96
    spec: 
      # 指定DNS的解析策略，有效值为: 'ClusterFirstWithHostNet', 'ClusterFirst', 'Default' or 'None'
      # 默认值为： ClusterFirst，表示以集群的DNS解析优先，特指的是我们的CoreDNS服务。
      # dnsPolicy:
      containers:
      - image: registry.cn-hangzhou.aliyuncs.com/yinzhengjie-k8s/apps:v1
        name: xiuxian
        
        
[root@master231 deployments]# kubectl apply -f 05-deploy-dnsPolicy.yaml
deployment.apps/deploy-xiuxian-dnspolicy created

#查看集群列表状态
[root@master231 deployments]# kubectl get pods -o wide
NAME                                       READY   STATUS    RESTARTS   AGE   IP               NODE        NOMINATED NODE   READINESS GATES
deploy-xiuxian-dnspolicy-9ddcfd7db-6mpsc   1/1     Running   0          3s    10.100.140.79    worker233   <none>           <none>
deploy-xiuxian-dnspolicy-9ddcfd7db-gfjbw   1/1     Running   0          3s    10.100.203.174   worker232   <none>           <none>
deploy-xiuxian-dnspolicy-9ddcfd7db-pctmz   1/1     Running   0          3s    10.100.203.176   worker232   <none>           <none>
deploy-xiuxian-dnspolicy-9ddcfd7db-rf8nw   1/1     Running   0          3s    10.100.140.78    worker233   <none>           <none>
deploy-xiuxian-dnspolicy-9ddcfd7db-zf5sn   1/1     Running   0          3s    10.100.140.77    worker233   <none>           <none>

#查看是否是默认的DNS策略
[root@master231 deployments]# kubectl get pods  -o yaml | grep dnsPolicy
    dnsPolicy: ClusterFirst
    dnsPolicy: ClusterFirst
    dnsPolicy: ClusterFirst
    dnsPolicy: ClusterFirst
    dnsPolicy: ClusterFirst
  
  
#进入容器，ping集群内任意一个svc资源
[root@master231 deployments]# kubectl exec -it deploy-xiuxian-dnspolicy-9ddcfd7db-6mpsc -- sh
/ # ping  ep-db 
PING ep-db (10.200.2.2): 56 data bytes
64 bytes from 10.200.2.2: seq=0 ttl=64 time=0.165 ms
^C
--- ep-db ping statistics ---
1 packets transmitted, 1 packets received, 0% packet loss
round-trip min/avg/max = 0.165/0.165/0.165 ms

#查看容器内部的DNS解析文件
/ # cat /etc/resolv.conf 
nameserver 10.200.0.10
search default.svc.oldboyedu.com svc.oldboyedu.com oldboyedu.com 
options ndots:5

二、使用了hostNetwork则默认的策略将会失效

1.作用

​ hostNetwork使用了宿主机网络，容器内的DNS也会使用宿主机的DNS

2.测试

[root@master231 deployments]# cat 05-deploy-dnsPolicy.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: deploy-xiuxian-dnspolicy
  labels:
    apps: xiuxian
spec:
  replicas: 1
  selector:
    matchLabels:
      version: v1
  template:
    metadata:
      labels:
        version: v1
        school: oldboyedu
        class: linux96
    spec: 
      # 指定DNS的解析策略，有效值为: 'ClusterFirstWithHostNet', 'ClusterFirst', 'Default' or 'None'
      # 默认值为： ClusterFirst，表示以集群的DNS解析优先，特指的是我们的CoreDNS服务。
      # dnsPolicy:
      hostNetwork: true
      containers:
      - image: registry.cn-hangzhou.aliyuncs.com/yinzhengjie-k8s/apps:v1
        name: xiuxian
        
        
[root@master231 deployments]# kubectl apply -f 05-deploy-dnsPolicy.yaml
deployment.apps/deploy-xiuxian-dnspolicy created


[root@master231 deployments]# kubectl get pods -o wide
NAME                                        READY   STATUS    RESTARTS   AGE   IP           NODE        NOMINATED NODE   READINESS GATES
deploy-xiuxian-dnspolicy-8564d5dc99-8sccq   1/1     Running   0          3s    10.0.0.233   worker233   <none>           <none>



[root@master231 deployments]# kubectl get pods  -o yaml | grep dnsPolicy
    dnsPolicy: ClusterFirst
[root@master231 deployments]# 
[root@master231 deployments]# kubectl exec -it deploy-xiuxian-dnspolicy-8564d5dc99-8sccq -- sh
/ # 
/ # cat /etc/resolv.conf 
nameserver 223.5.5.5
nameserver 223.6.6.6
search 
/ # 
/ #  ping  ep-db 
ping: bad address 'ep-db'
/ # 

三、修改策略为ClusterFirstWithHostNet

1.作用

​ 'ClusterFirstWithHostNet'一般情况下会和"hostNetwork: true"搭配使用，还是优先使用K8S集群的CoreDNS.

​ 当 Pod 使用 hostNetwork: true 时，Pod 会共享宿主机的网络命名空间。默认情况下，这样的 Pod 会继承宿主机的 DNS 配置，从而无法直接使用 Kubernetes 集群内部的 DNS 服务。而 ClusterFirstWithHostNet 策略允许这些 Pod 优先使用 Kubernetes 集群内部的 DNS 服务来解析集群内部的域名，同时也能解析外部域名

2.测试

[root@master231 deployments]# cat 05-deploy-dnsPolicy.yaml 
apiVersion: apps/v1
kind: Deployment
metadata:
  name: deploy-xiuxian-dnspolicy
  labels:
    apps: xiuxian
spec:
  replicas: 1
  selector:
    matchLabels:
      version: v1
  template:
    metadata:
      labels:
        version: v1
        school: oldboyedu
        class: linux96
    spec: 
      # 指定DNS的解析策略，有效值为: 'ClusterFirstWithHostNet', 'ClusterFirst', 'Default' or 'None'
      # 默认值为： ClusterFirst，表示以集群的DNS解析优先，特指的是我们的CoreDNS服务。
      # 其中'ClusterFirstWithHostNet'一般情况下会和"hostNetwork: true"搭配使用，还是优先使用K8S集群的CoreDNS
      dnsPolicy: ClusterFirstWithHostNet
      hostNetwork: true
      containers:
      - image: registry.cn-hangzhou.aliyuncs.com/yinzhengjie-k8s/apps:v1
        name: xiuxian
        
        
        
[root@master231 deployments]# kubectl get pods -o wide
NAME                                        READY   STATUS    RESTARTS   AGE   IP           NODE        NOMINATED NODE   READINESS GATES
deploy-xiuxian-dnspolicy-6d8fd88c4b-cz2jv   1/1     Running   0          5s    10.0.0.233   worker233   <none>           <none>
[root@master231 deployments]# 
[root@master231 deployments]# kubectl get pods  -o yaml | grep dnsPolicy
    dnsPolicy: ClusterFirstWithHostNet
[root@master231 deployments]# 
[root@master231 deployments]# kubectl exec -it deploy-xiuxian-dnspolicy-6d8fd88c4b-cz2jv -- sh
/ # cat /etc/resolv.conf 
nameserver 10.200.0.10
search default.svc.oldboyedu.com svc.oldboyedu.com oldboyedu.com 
options ndots:5
/ # 
/ # ping ep-db
PING ep-db (10.200.2.2): 56 data bytes
64 bytes from 10.200.2.2: seq=0 ttl=64 time=0.303 ms
64 bytes from 10.200.2.2: seq=1 ttl=64 time=0.109 ms
^C
--- ep-db ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max = 0.109/0.206/0.303 ms
/ #