服务类型为NodePort并同时指定了port和targetPort意味着什么？

Question

spec:
  type: NodePort
  ports:
  - port: 27018
    targetPort: 27017
    protocol: TCP

nodePort     The port on each node on which this service is exposed when type=NodePort or LoadBalancer. Usually
integer      assigned by the system. If specified, it will be allocated to the service if unused or else creation of the
             service will fail. Default is to auto-allocate a port if the ServiceType of this Service requires one. More info: 
             http://kubernetes.io/docs/user-guide/services#type--nodeport

port         The port that will be exposed by this service.
integer

targetPort   Number or name of the port to access on the pods targeted by the service. Number must be in the range 1
IntOrString  to 65535. Name must be an IANA_SVC_NAME. If this is a string, it will be looked up as a named port in the
             target Pod's container ports. If this is not specified, the value of the 'port' field is used (an identity map).
             This field is ignored for services with clusterIP=None, and should be omitted or set equal to the 'port' field.
             More info: http://kubernetes.io/docs/user-guide/services#defining-a-service

我的理解是，集群之外的客户机将“看到”的端口将是文档中定义的30000-32767范围内动态分配的端口。这将使用一些我还不明白的魔法流到给定节点上的targetport（在本例中是27017)。

那么这里的端口用于什么呢？

Answer 1

为了更好地解释这个概念，我将服务的NodePort概念可视化。

正如@Fishi在他的回答中提到的，NodePort允许向外部客户端公开k8s主机端口（也就是NodePort)。客户机可以直接访问nodeport，k8s将通信转发到必要的端口。

K8s在其所有节点上保留一个nodeport。所有运行服务的节点都打开此端口。