Kubernetes Headless Service

1. Headless Service

headless service 需要将 spec.clusterIP 设置成 None。

因为没有ClusterIP，kube-proxy 并不处理此类服务，因为没有load balancing或 proxy 代理设置，在访问服务的时候回返回后端的全部的Pods IP地址，主要用于开发者自己根据pods进行负载均衡器的开发(设置了selector) 或 StatefulSet.

2. Test Headless Service With selectors

$cat deployment.yaml
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  replicas: 2 # tells deployment to run 2 pods matching the template
  template: # create pods using pod definition in this template
    metadata:
      # unlike pod-nginx.yaml, the name is not included in the meta data as a unique name is
      # generated from the deployment name
      labels:
        app: nginx_test
    spec:
      containers:
      - name: nginx
        image: nginx:1.7.9
        ports:
        - containerPort: 80

$ cat headless_service.yaml
kind: Service
apiVersion: v1
metadata:
  name: nginx-service
spec:
  selector:
    app: nginx_test
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80
  clusterIP: None

通过dns访问，会返回后端pods的列表

登录到Cluster的内部pod

nslookup nginx-service
nslookup: can't resolve '(null)': Name does not resolve

Name:      nginx-service
Address 1: 10.10.23.36
Address 2: 10.10.23.39