DNS Configuration_Cloud Container Engine_Huawei Cloud

scenario

Kubernetes in-cluster Kube-DNS/CoreDNS applies to resolving only cluster-internal domain names or cluster-internal domain names + external domain names. This is the default DNS for workloads.

example :

apiversion : v1 is kind 
 kind : Pod 
 metadata : 
   namespace : default 
   name : dns - example 
 spec : 
   container : 
   - name : test 
     image : nginx : alpine 
   dnspolicy : ClusterFirst 
   imagePullSecrets : 
     - name : default - secret

Container’s DNS configuration file:

nameserver 10.247.3.10
search default.svc.cluster.local svc.cluster.local cluster.local
options ndots:5

scenario

By default , a dns is used for workload run with hostNetwork . If workload need to use Kube – DNS / CoreDNS , set dnspolicy to ClusterFirstWithHostNet .

example :

apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  hostNetwork: true
  dnsPolicy: ClusterFirstWithHostNet
  containers:
  - name: nginx
    image: nginx:alpine
    ports:
    - containerPort: 80
  imagePullSecrets:
    - name: default-secret

Container’s DNS configuration file:

nameserver 10.247.3.10
search default.svc.cluster.local svc.cluster.local cluster.local
options ndots:5

scenario

You can flexibly customize the DNS configuration file for applications. Using dnsPolicy and dnsConfig together can address almost all scenarios, including the scenarios in which an on-premises DNS will be used, multiple DNSs will be cascaded, and DNS configuration options will be modified.

Example 1: Using Your On-Premises DNS

set dnspolicy to None so application ‘s dns configuration file is generate base on dnsConfig .

apiversion : v1 is kind 
 kind : Pod 
 metadata : 
   namespace : default 
   name : dns - example 
 spec : 
   container : 
   - name : test 
     image : nginx : alpine 
   dnspolicy : " None " 
   dnsconfig : 
     nameserver : 
     - 10.2.3.4   # ip address of your on - premise DNS 
     search : 
     - ns1.svc.cluster.local 
     - my.dns.search.suffix 
     option : 
     - name : ndot 
       value : " 2 " 
     - name : timeout 
       value : " 3 " 
   imagePullSecrets : 
     - name : default - secret

Container’s DNS configuration file:

nameserver 10.2.3.4
search ns1.svc.cluster.local my.dns.search.suffix
options timeout:3 ndots:2

Example 2: Modifying the ndots Option in the DNS Configuration File to Reduce Invalid DNS Queries

set dnspolicy to a value other than None so the dns parameter configure in dnsConfig are add to the dns configuration file generate base on dnsPolicy .

apiVersion: v1
kind: Pod
metadata:
  namespace: default
  name: dns-example
spec:
  containers:
  - name: test
    image: nginx:alpine
  dnsPolicy: "ClusterFirst"
  dnsConfig:
    options:
    - name: ndots
      value: "2" # The ndots:5 option in the DNS configuration file generated based on the ClusterFirst policy is changed to ndots:2.
  imagePullSecrets:
    - name: default-secret

Container’s DNS configuration file:

nameserver 10.247.3.10
search default.svc.cluster.local svc.cluster.local cluster.local
options ndots:2

Example 3: Using Multiple DNSs in Serial Sequence

apiVersion: v1
kind: Pod
metadata:
  namespace: default
  name: dns-example
spec:
  containers:
  - name: test
    image: nginx:alpine
  dnsPolicy: ClusterFirst  # Added DNS configuration. The cluster connects to CoreDNS by default.
  dnsConfig:
    nameservers:
    - 10.2.3.4 # IP address of your on-premises DNS
  imagePullSecrets:
    - name: default-secret

A maximum of three dns address can be configure for a nameserver in the container dns configuration file .

• If dnsPolicy is set to ClusterFirst and the cluster uses CoreDNS, you can add two custom DNS addresses in addition to the CoreDNS address. Excess DNS addresses are invalid.
• If dnsPolicy is set to ClusterFirst and the cluster uses CoreDNS and NodeLocal DNSCache, you can add one custom DNS address in addition to the CoreDNS and NodeLocal DNSCache addresses. Excess DNS addresses are invalid.

Container’s DNS configuration file:

nameserver 10.247.3.10 10.2.3.4
search default.svc.cluster.local svc.cluster.local cluster.local
options ndots:5