Kubernetes - Headless Service

DevOps/Kubernetes

Kubernetes - Headless Service

yscho03 2021. 11. 30. 16:19

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Headless Service

정의

ClusterIP가 없는 서비스로 단일 진입점이 필요 없을 때 사용
Service와 연결된 Pod의 endpoint로 DNS 레코드가 생성됨

쿠버네티스 coreDNS에 등록되며 DNS resolving Service로 요청이 가능해진다.

Pod의 DNS 주소: pod-ip-addr.namespace.pod.cluster.local

생성

사전에 Deployment를 먼저 생성하고 그 다음에 Service를 생성하여 묶어준다.

root@master:~# cat > deploy-nginx.yaml 
apiVersion: apps/v1
kind: Deployment
metadata:
  name: webui
spec:
  replicas: 3
  selector:
    matchLabels:
      app: webui
  template:
    metadata:
      name: nginx-pod
      labels:
        app: webui
    spec:
      containers:
      - name: nginx-container
        image: nginx:1.14
		
root@master:~# kubectl create -f deploy-nginx.yaml 
deployment.apps/webui create
root@master:~# kubectl get pods -o wide
NAME                     READY   STATUS    RESTARTS     AGE    IP          NODE                NOMINATED NODE   READINESS GATES
testpod                  1/1     Running   1 (6s ago)   107s   10.36.0.2   node1.example.com   <none>           <none>
webui-6d4c4cc4b8-6mzj8   1/1     Running   0            22m    10.44.0.1   node2.example.com   <none>           <none>
webui-6d4c4cc4b8-m8g4f   1/1     Running   0            22m    10.36.0.1   node1.example.com   <none>           <none>
webui-6d4c4cc4b8-vhj96   1/1     Running   0            22m    10.44.0.2   node2.example.com   <none>           <none>
				
root@master:~# cat > headless-service.yaml
apiVersion: v1
kind: Service
metadata:
  name: headless-service
spec:
  type: ClusterIP
  clusterIP: None
  selector:
    app: webui
  ports:
  - protocol: TCP
    port: 80
    targetPort: 80
root@master:~# kubectl create -f headless-service.yaml 
service/headless-service created

조회

root@master:~# kubectl get svc -o wide
NAME               TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE    SELECTOR
headless-service   ClusterIP   None         <none>        80/TCP    9s     app=webui
kubernetes         ClusterIP   10.96.0.1    <none>        443/TCP   117m   <none>

root@master:~# kubectl describe svc headless-service 
Name:              headless-service
Namespace:         default
Labels:            <none>
Annotations:       <none>
Selector:          app=webui
Type:              ClusterIP
IP Family Policy:  SingleStack
IP Families:       IPv4
IP:                None
IPs:               None
Port:              <unset>  80/TCP
TargetPort:        80/TCP
Endpoints:         10.36.0.1:80,10.44.0.1:80,10.44.0.2:80
Session Affinity:  None
Events:            <none>

확인

centos pod를 생성하고 파드 안으로 진입하여 도메인 (pod-ip-addr.namespace.pod.cluster.local) 을 호출해본다.

root@master:~# kubectl run testpod -it --image=centos:7
If you dont see a command prompt, try pressing enter.

[root@testpod /]# cat /etc/resolv.conf 
nameserver 10.96.0.10
search default.svc.cluster.local svc.cluster.local cluster.local
options ndots:5

[root@testpod /]# curl 10-44-0-01.default.pod.cluster.local
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
    body {
        width: 35em;
        margin: 0 auto;
        font-family: Tahoma, Verdana, Arial, sans-serif;
    }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

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