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Service ports in k8s

targetPort must equal containerPort

nodePort -> port -> targetPort = containerPort

1. External Traffic Flow (User → Pod)​

2. ClusterIP Service (Inter-Pod Communication)​

3. All Service Types Comparison​

4. Real Example with All Port Numbers​

Key Concepts Explained​

Port Types:​

  1. containerPort (Pod spec)

    • Port your application actually listens on inside the container
    • This is just documentation; the container exposes whatever port the app uses

  2. targetPort (Service spec)

    • Which port on the Pod to forward traffic to
    • Must match the containerPort (or the actual port your app uses)
    • Defaults to the same value as port if not specified

  3. port (Service spec)

    • Port the Service listens on (within the cluster)
    • What other pods use to reach this service

  4. nodePort (NodePort/LoadBalancer Service)

    • Port exposed on every node's IP (range: 30000-32767)
    • Allows external access via NodeIP:nodePort

5. DNS Resolution Flow​

Practical Example​

# Pod with containerPort
apiVersion: v1
kind: Pod
metadata:
  name: nginx-pod
  labels:
    app: nginx
spec:
  containers:
    - name: nginx
      image: nginx:1.21
      ports:
        - containerPort: 80
          name: http

---
# ClusterIP Service
apiVersion: v1
kind: Service
metadata:
  name: nginx-clusterip
spec:
  type: ClusterIP
  selector:
    app: nginx
  ports:
    - port: 8080
      targetPort: 80
      name: http

---
# NodePort Service
apiVersion: v1
kind: Service
metadata:
  name: nginx-nodeport
spec:
  type: NodePort
  selector:
    app: nginx
  ports:
    - port: 8080
      targetPort: 80
      nodePort: 30080
      name: http