k8s-dns设置

​ 参考链接：https://kubernetes.io/zh/docs/concepts/services-networking/dns-pod-service/

​ 清除 Pod 预设 DNS 配置，当 dnsPolicy 设置成为这个值之后， kubernetes 不会为 Pod 预先加载任何逻辑用于判定得到 DNS 的配置。因此若将 dnsPolicy 设置为 None , 为了避免 Pod 里面没有 DNS 配置，最好通过 dnsConfig 来描述自定义的 DNS 参数。如下所示：

apiVersion: v1
kind: Pod
metadata: 
  name: busybox-test
spec:
  restartPolicy: onFailure
  dnsPolicy: None
  dnsConfig:
    nameservers: 
    - 114.114.114.114
    - 8.8.8.8
    searches:
    - test.svc.cluster.local
    options:
    - name: ndots
      value: "5"
  containers:
  - name: busybox
    image: busybox:1.28
    imagePullPolicy: IfNotPresent
    command:
    - "sleep"
    - "600"

# 查看dns配置
[root@k8s-master-1 learn]# kubectl exec busybox-test -- cat /etc/resolv.conf
nameserver 114.114.114.114
nameserver 8.8.8.8
search test.svc.cluster.local
options ndots:5

​ Pod 里面的 DNS 配置继承了宿主机上的 DNS 配置。即，该 Pod 的 DNS 配置与宿主机完全一致。默认是使用ClusterFirst

apiVersion: v1
kind: Pod
metadata: 
  name: busybox-test
spec:
  restartPolicy: onFailure
  dnsPolicy: Default
  containers:
  - name: busybox
    image: busybox:1.28
    imagePullPolicy: IfNotPresent
    command:
    - "sleep"
    - "600"

# 查看宿主机dns信息
[root@k8s-master-1 learn]# cat /etc/resolv.conf
# Generated by NetworkManager
nameserver 8.8.8.8
nameserver 114.114.114.114

# 查看busybox-test内dns信息
[root@k8s-master-1 learn]# kubectl exec busybox-test -- cat /etc/resolv.conf
nameserver 8.8.8.8
nameserver 114.114.114.114

​ 与 Default 相反，会预先使用 kube-dns (或 CoreDNS ) 的信息当预设置参数写入到该 Pod 内的DNS配置，k8s默认使用这个模式

apiVersion: v1
kind: Pod
metadata: 
  name: busybox-test
spec:
  restartPolicy: onFailure
  dnsPolicy: ClusterFirst
  containers:
  - name: busybox
    image: busybox:1.28
    imagePullPolicy: IfNotPresent
    command:
    - "sleep"
    - "600"

# 查看busybox-test内dns信息
[root@k8s-master-1 learn]# kubectl exec busybox-test -- cat /etc/resolv.conf
nameserver 10.0.0.10
search default.svc.cluster.local. svc.cluster.local. cluster.local.
options ndots:5

注：

1. 设置 hostNetwork = true 之后，会让 Pod 与该节点公用相同的网络空间(网卡/路由等)
2. 如设置了 hostNetwork = true 时，ClusterFirst 会被强制转化为 Default 。如下：

[root@k8s-master-1 learn]# cat pod.yaml 
apiVersion: v1
kind: Pod
metadata: 
  name: busybox-test
spec:
  restartPolicy: onFailure
  dnsPolicy: ClusterFirst
  hostNetwork: true
  containers:
  - name: busybox
    image: busybox:1.28
    imagePullPolicy: IfNotPresent
    command:
    - "sleep"
    - "600"

[root@k8s-master-1 learn]# kubectl exec busybox-test -- cat /etc/resolv.conf
nameserver 8.8.8.8
nameserver 114.114.114.114

这种情况下的POD，既能用host的DNS服务，又能使用集群内,需要将hostNetwork打开

同时使用 hostNetwork 与 kube-dns 作为 Pod 预设 DNS 配置。

apiVersion: v1
kind: Pod
metadata: 
  name: busybox-test
spec:
  restartPolicy: onFailure
  dnsPolicy: ClusterFirstWithHostNet
  hostNetwork: true
  containers:
  - name: busybox
    image: busybox:1.28
    imagePullPolicy: IfNotPresent
    command:
    - "sleep"
    - "600"

[root@k8s-master-1 learn]# kubectl exec busybox-test -- cat /etc/resolv.conf
nameserver 10.0.0.10
search default.svc.cluster.local. svc.cluster.local. cluster.local.
options ndots:5

To have DNS options set along with hostNetwork, you have to specify DNS policy explicitly to 'ClusterFirstWithHostNet'. # 如果不加上dnsPolicy: ClusterFirstWithHostNet ，pod默认使用所在宿主主机使用的DNS，这样也会导致容器内不能通过service name 访问k8s集群中其他POD

# pod内增加域名解析
[root@k8s-master-1 learn]# cat pod.yaml 
apiVersion: v1
kind: Pod
metadata: 
  name: busybox-test
spec:
  hostAliases:
  - hostnames: 
    - www.baidu.com
    - baidu.com
    ip: 103.235.46.39
  containers:
  - name: busybox
    image: busybox:1.28
    command:
    - "sleep"
    - "600"

# 结果,查看容器的/etc/hosts,自定义域名
[root@k8s-master-1 learn]# kubectl exec busybox-test -- cat /etc/hosts
# Kubernetes-managed hosts file.
127.0.0.1	localhost
::1	localhost ip6-localhost ip6-loopback
fe00::0	ip6-localnet
fe00::0	ip6-mcastprefix
fe00::1	ip6-allnodes
fe00::2	ip6-allrouters
10.70.2.4	busybox-test

# Entries added by HostAliases.
103.235.46.39	www.baidu.com	baidu.com