Service Discovery

Key Takeaways

The Service primitive in Kubernetes abstracts away network complexities and provides a durable endpoint for accessing pods.

NodePort Service

Allows external access to the Kubernetes network by exposing a static port on the node (range: 30000-32767).

apiVersion: v1
kind: Service
metadata:
  name: grade-submission-portal
spec:
  type: NodePort
  selector:
    app: grade-submission-portal
  ports:
    - port: 8080
      targetPort: 8080
      nodePort: 30080

• The external request is initiated on the node's static port (nodePort: 30080).
• The request enters the cluster through the Service's internal port (port: 8080). With NodePort services, this internal port can be any valid port number, as the external nodePort (30080) will be mapped to whatever internal port is specified.
• The service acts as a proxy by directing the request to a matching pod using a label selector.
• The service specifies a target port (targetPort: 8080) that ensures the request reaches the container port on the pod.

Note: The NodePort service is often used when prototyping, rarely in practice.

ClusterIP Service

Used for internal pod-to-pod communication within the cluster.

apiVersion: v1
kind: Service
metadata:
  name: backend-service
spec:
  type: ClusterIP
  selector:
    app: backend
  ports:
    - port: 8080
      targetPort: 8080

• Pods within the cluster can access the service using its name (backend-service) and service's internal port (port: 8080).
• The service acts as a proxy by directing the request to a matching pod using a label selector.
• The service specifies a target port (targetPort: 8080) that ensures the request reaches the container port on the pod.