AKS load balancer service accessible on wrong port

Question

I have a simple ASP.NET core Web API. It works locally. I deployed it in Azure AKS using the following yaml:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: sa-be
spec:
  selector:
    matchLabels:
      name: sa-be
  template:
    metadata:
      labels:
        name: sa-be
    spec:
      nodeSelector:
        kubernetes.io/os: linux
      containers:
      - name: sa-be
        image: francotiveron/anapi:latest
        resources:
          limits:
            memory: "64Mi"
            cpu: "250m"
---
apiVersion: v1
kind: Service
metadata:
  name: sa-be-s
spec:
  type: LoadBalancer
  selector:
    name: sa-be
  ports:
  - port: 8080
    targetPort: 80

The result is:

> kubectl get service sa-be-s
NAME      TYPE           CLUSTER-IP     EXTERNAL-IP     PORT(S)          AGE
sa-be-s   LoadBalancer   10.0.157.200   20.53.188.247   8080:32533/TCP   4h55m



> kubectl describe service sa-be-s 
Name:                     sa-be-s
Namespace:                default
Labels:                   
Annotations:              
Selector:                 name=sa-be
Type:                     LoadBalancer
IP Families:              
IP:                       10.0.157.200
IPs:                      
LoadBalancer Ingress:     20.53.188.247
Port:                       8080/TCP
TargetPort:               80/TCP
NodePort:                   32533/TCP
Endpoints:                10.244.2.5:80
Session Affinity:         None
External Traffic Policy:  Cluster
Events:

I expected to reach the Web API at http://20.53.188.247:32533/, instead it is reachable only at http://20.53.188.247:8080/

Can someone explain

Is this is he expected behaviour
If yes, what is the use of the NodePort (32533)?

user_9929015 · Answer

Yes, expected. Explained: Kubernetes Service Ports - please read full article to understand what is going on in the background.

Loadbalancer part:

apiVersion: v1
kind: Service
metadata:
  name: sa-be-s
spec:
  type: LoadBalancer
  selector:
    name: sa-be
  ports:
  - port: 8080
    targetPort: 80

port is the port the cloud load balancer will listen on (8080 in our example) and targetPort is the port the application is listening on in the Pods/containers. Kubernetes works with your cloud’s APIs to create a load balancer and everything needed to get traffic hitting the load balancer on port 8080 all the way back to the Pods/containers in your cluster listening on targetPort 80.

now main: Behind the scenes, many implementations create NodePorts to glue the cloud load balancer to the cluster. The traffic flow is usually like this.

AKS load balancer service accessible on wrong port

1 Answers