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NodePort Services

A NodePort service allows you to expose a service (externally) by opening a specific port on every node in the cluster.

Any requests made through the node will be routed to the service, even if the node doesn't handle the service.

A NodePort service opens a specific port on all nodes. Traffic to the nodePort (30123) will be routed to the targetPort (8080) of the pods that handle the service.
A NodePort service opens a specific port on all nodes. Traffic to the nodePort (30123) will be routed to the targetPort (8080) of the pods that handle the service. (Source: Lukša)

NodePort service descriptor

Mention the service's selector, and the ports mapping.

apiVersion: v1
kind: Service
metadata:
  name: kubia-nodeport
spec:
  type: NodePort
  # pods that handle the service have these labels
  selector:
    app: kubia
  ports:
    - # connect here if you use the service's internal IP
      port: 80
      # connect here if you use a cluster node's IP
      nodePort: 30123
      # traffics will be routed here
      targetPort: 8080

Connecting to a NodePort service

Ensure that you have allowed external connections to your nodes on the specified port.

When you list your NodePort service,

kubectl get svc kubia-nodeport
# NAME             CLUSTER-IP       EXTERNAL-IP   PORT(S)        AGE
# kubia-nodeport   10.111.254.223   <nodes>       80:30123/TCP   2m

Observe that:

  • The EXTERNAL-IP column — lists <nodes>, which means you can connect to the service using any of the cluster node's IP
  • The PORT(S) column — lists the "internal port" and the "node port":
    • internal port 80, if you want to connect from the service's cluster-internal IP (in this case, 10.111.254.223)
    • node port 30123, if you want to connect from the cluster node's IP

In other words, this means that you can connect to your service through:

  • 10.111.254.223 port 80
  • <1st node's IP> port 30123
  • <2nd node's IP> port 30123
  • and so on

References