[K8s]DNS

K8s DNS

• Service 및 pod용 DNS
• Cluster에서 실행하는 모든 pod가 사용할 수 있도록 구성
• DNS를 통해 service와 pod access
  • service_name.namespace.svc.cluster.local
  • Pod-IP-Address.namespace.pod.cluster.local

<이미지 출처 : https://www.youtube.com/watch?v=vhsyWMnc2f8&list=PLApuRlvrZKohLYdvfX-UEFYTE7kfnnY36&index=8>

 

• kube-dns service 작동 확인

kubectl get service --all-namespaces

NAMESPACE     NAME         TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)                  AGE
default       kubernetes   ClusterIP   10.96.0.1    <none>        443/TCP                  4d20h
kube-system   kube-dns     ClusterIP   10.96.0.10   <none>        53/UDP,53/TCP,9153/TCP   4d20h

• coreDNS pod 작동 확인

kubectl get pods --all-namespaces

NAMESPACE     NAME                                         READY   STATUS    RESTARTS        AGE
kube-system   coredns-6d4b75cb6d-gd65q                     1/1     Running   4 (3h26m ago)   4d20h
kube-system   coredns-6d4b75cb6d-pr92v                     1/1     Running   4 (3h26m ago)   4d20h
...

CoreDNS 사용

• pod 배포 및 service 생성, 확인

vi deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web
spec:
  replicas: 3
  selector:
    matchLabels:
      app: web
  template:
    metadata:
      name: nginx-pod
      labels:
        app: web
    spec:
      containers:
      - name: nginx-container
        image: nginx:1.14

vi svc.yaml

apiVersion: v1
kind: Service
metadata:
  name: svc-web
spec:
  clusterIP: 10.96.100.100
  selector:
    app: web
  ports:
  - protocol: TCP
    port: 80
    targetPort: 80

kubectl apply -f deployment.yaml
kubectl apply -f svc.yaml

kuebctl get all

• client용 pod 실행 및 nameserver 확인
  • kube-dns의 ip주소와 동일

kubectl run client-pod --image=centos:7 -it -- /bin/bash

cat /etc/resolv.conf

search default.svc.cluster.local svc.cluster.local cluster.local t4loxwhes1oetkkxir4bjy3yxf.syx.internal.cloudapp.net
nameserver 10.96.0.10
options ndots:5

• Service에 대한 coreDNS 사용

curl svc-web.default.svc.cluster.local
curl svc-web

• Pod에 대한 coreDNS 사용

curl 10-47-0-1.default.pod.cluster.local

 

Pod내 DNS 설정

• dnsconfig pod 생성
  • https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/#pod-dns-config 참고

vi custom-dns.yaml

apiVersion: v1
kind: Pod
metadata:
  namespace: default
  name: dns-example
spec:
  containers:
    - name: test
      image: nginx
  dnsPolicy: "None"
  dnsConfig:
    nameservers:
      - 1.2.3.4                           # 변경 가능
    searches:
      - ns1.svc.cluster-domain.example    # 변경 가능
      - my.dns.search.suffix
    options:
      - name: ndots
        value: "2""
      - name: edns0

• 생성한 pod로 접속
  • dnsconfig와 일치

kubectl exec dns-example -it -- /bin/bash

cat /etc/resolv.conf

search ns1.svc.cluster-domain.example my.dns.search.suffix
nameserver 1.2.3.4
options ndots:2 edns0

 

 

참고 :

https://www.youtube.com/watch?v=vhsyWMnc2f8&list=PLApuRlvrZKohLYdvfX-UEFYTE7kfnnY36&index=8