How to make use of Kubernetes port names?

Question

In a kubernetes deployment I specify a port like so:

 containers:
 - name: nginx
   image: nginx:latest
   ports:
    - name: nginx-port
      containerPort: 80
      protocol: TCP

Now in a service I can reference that port like so (allows me to only specify the external port in the service):

spec:
  type: ClusterIP
  ports:
  - name: nginx-port
    port: 80
    targetPort: nginx-port
    protocol: TCP

Now the question, can I reference service and port elsewhere using the following syntax nginx-service.default.svc.cluster.local:nginx-port? You know I can make reference to services using this special names, but I find myself hardcoding the port number like so nginx-service.default.svc.cluster.local:80.

Answer 1

Usually, you refer to a target port by its number. But you can give a specific name to each pod`s port and refer to this name in your service specification.

This will make your service clearer. Here a small example:

apiVersion: v1 kind: Pod metadata:   name: named-port-pod   labels:     app: named-port-pod spec:   containers:     - name: echoserver       image: gcr.io/google_containers/echoserver:1.4       ports:       - name: pod-custom-port         containerPort: 8080 --- apiVersion: v1 kind: Service metadata:   name: named-port-svc spec:   ports:     - port: 80       targetPort: pod-custom-port   selector:     app: named-port-pod 

Answer 2

Kubernetes DNS service provides SRV records for all named ports of services using below format

_my-port-name._my-port-protocol.my-svc.my-namespace.svc.cluster-domain.example

In your case, you should be able to access it by querying below domain

_nginx-port._tcp.nginx-service.default.svc.cluster.local

Example

nslookup -type=SRV _nginx-port._tcp.nginx-service.default.svc.cluster.local

And the result:

_nginx-port._tcp.nginx-service.default.svc.cluster.local   service = 0 100 80 nginx-service.default.svc.cluster.local.

In the above output, nginx-service.default.svc.cluster.local is the target domain and 80 is the target port that you should connect to, i.e. nginx-service.default.svc.cluster.local:80