Services: ClusterIP, NodePort, LoadBalancer

Key points

• Pod IPs change constantly. A Service is a stable virtual IP and DNS name in front of a moving set of pods.
• It selects pods by label, not by Deployment. Endpoints update automatically as pods come and go.
• ClusterIP is the default and is internal only. Reach it as orders, or orders.prod.svc.cluster.local from another namespace.
• NodePort opens one port in the 30000-32767 range on every node. Useful in dev, blunt in production.
• LoadBalancer asks the cloud for a real load balancer, one per Service, so the bill adds up fast.
• clusterIP: None makes it headless. DNS then returns the pod IPs directly, which is what StatefulSets use.

Example

apiVersion: v1
kind: Service
metadata:
  name: orders
spec:
  type: ClusterIP          # default: reachable only inside the cluster
  selector:
    app: orders            # matches pod labels, not the Deployment name
  ports:
    - port: 80             # the Service port
      targetPort: 8080     # the container port
---
apiVersion: v1
kind: Service
metadata:
  name: orders-public
spec:
  type: LoadBalancer       # cloud provisions an external IP
  selector:
    app: orders
  ports:
    - port: 443
      targetPort: 8080

A Service turns a churning set of pods into one name that never changes.