定于spec:clusterIP: None
还记得Service的Cluster IP是做什么的吗？对，一个Service可能对应多个EndPoint(Pod)，client访问的是Cluster IP，通过iptables规则转到Real Server，从而达到负载均衡的效果（实现原理请见这里）。如下：
有头service
kubectl get service NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE nginx-service 10.107.124.218 192.168.128.158 80/TCP,443/TCP 1d
kubectl describe service nginx-service Name: nginx-service Namespace: default Labels: Selector: component=nginx Type: ClusterIP IP: 10.107.124.218 External IPs: 192.168.128.158 Port: nginx-http 80/TCP Endpoints: 10.244.2.9:80 Port: nginx-https 443/TCP Endpoints: 10.244.2.9:443
nslookup nginx-service.default.svc.cluster.local 10.96.0.10 #这个ip为k8s dns的ip
Server: 10.96.0.10
Address: 10.96.0.10#53
Name: nginx-service.default.svc.cluster.local
Address: 10.107.124.218
虽然service有2个endpoint，但是dns查询时只会返回service的地址。具体client访问的是哪个Real Server，是由iptables来决定的。
无头service
kubectl get service NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE nginx None 80/TCP 1h
kubectl describe service nginx Name: nginx Namespace: default Labels: app=nginx Selector: app=nginx Type: ClusterIP IP: None Port: web 80/TCP Endpoints: 10.244.2.17:80,10.244.2.18:80 #通过web获取到pod的ip地址
nslookup nginx.default.svc.cluster.local 10.96.0.10 Server: 10.96.0.10 Address: 10.96.0.10#53 Name: nginx.default.svc.cluster.local Address: 10.244.2.17 Name: nginx.default.svc.cluster.local Address: 10.244.2.18
dns查询会如实的返回2个真实的endpoint