What does it mean for a Service to be of type NodePort, and have both port and targetPort specified? : <p>I am becoming more familiar with Kubernetes by the day, but am still at a basic level.  I am also not a networking guy.</p>

<p>I am staring at the following snippet of a Service definition, and I can't form the right picture in my mind of what is being declared:</p>

<pre><code>spec:
  type: NodePort
  ports:
  - port: 27018
    targetPort: 27017
    protocol: TCP
</code></pre>

<p>Referencing the <a href="https://kubernetes.io/docs/resources-reference/v1.5/#serviceport-v1" rel="noreferrer">ServicePort documentation</a>, which reads in part:</p>

<pre><code>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
</code></pre>

<p>My understanding is that the port that a client outside of the cluster will "see" will be the dynamically assigned one in the range of <code>30000</code>-<code>32767</code>, as defined <a href="https://kubernetes.io/docs/user-guide/services/#type-nodeport" rel="noreferrer">in the documentation</a>.  This will, using some black magic that I do not yet understand, flow to the <code>targetPort</code> on a given node (<code>27017</code> in this case).</p>

<p>So what is the <code>port</code> used for here?  </p>
