port
The port that the service is exposed on the service’s cluster ip (virsual ip). Port is the service port which is accessed by others with cluster ip.
即，这里的port表示：service暴露在cluster ip上的端口，<cluster ip>:port 是提供给集群内部客户访问service的入口。
nodePort
On top of having a cluster-internal IP, expose the service on a port on each node of the cluster (the same port on each node). You'll be able to contact the service on any<nodeIP>:nodePortaddress. So nodePort is alse the service port which can be accessed by the node ip by others with external ip.
首先，nodePort是kubernetes提供给集群外部客户访问service入口的一种方式（另一种方式是LoadBalancer），所以，<nodeIP>:nodePort 是提供给集群外部客户访问service的入口。
targetPort
The port on the pod that the service should proxy traffic to.
targetPort很好理解，targetPort是pod上的端口，从port和nodePort上到来的数据最终经过kube-proxy流入到后端pod的targetPort上进入容器。
转： http://blog.csdn.net/xinghun_4/article/details/50492041