ClusterIP

Learn the ClusterIP service type.

ClusterIP

ClusterIP is the default Service type: it gives a virtual IP reachable only from inside the cluster. It's used for internal communication between applications (API → database). In the YAML, port is what the service listens on, and targetPort is the container port on the pod:

apiVersion: v1
kind: Service
metadata:
  name: web
spec:
  selector:
    app: web
  ports:
    - port: 80
      targetPort: 8080

Service DNS names

The cluster DNS (CoreDNS) creates a record for each service in the form name.namespace.svc.cluster.local. From the same namespace the short name is enough, from another namespace name.namespace:

$ kubectl run -it --rm dns-test --image=busybox:1.36 --restart=Never -- nslookup web
Name:      web.default.svc.cluster.local
Address:   10.96.45.12
# from another namespace: http://web.default

A headless service, written with clusterIP: None, gets no virtual IP; DNS returns the pod IPs directly (used with StatefulSets).

Exercise A ClusterIP service

Write a Service YAML: name web; selector app: web; a single port: port: 80, targetPort: 8080. (If no type is written, it is ClusterIP.)

Show example solution

apiVersion: v1
kind: Service
metadata:
  name: web
spec:
  selector:
    app: web
  ports:
    - port: 80
      targetPort: 8080

Test yourself

How is a request sent to this service from another pod?
- http://web:80 (or http://web)
- http://web:8080
- http://localhost:80
- With the host's IP
Show answer

http://web:80 (or http://web) — The client uses the service port (80); the service forwards it to the pod's 8080.

Specify the container port on the pod.

  ports:
    - port: 80
      ____: 8080

Show answer

  ports:
    - port: 80
      targetPort: 8080

Match.

ClusterIP

Cluster-internal only
port

The service port
targetPort

The pod port
clusterIP: None

Headless service

Next lesson: NodePort

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