ClusterIP Services

ClusterIP is the default Service type, reachable only from inside the cluster.

Syntaxspec: type: ClusterIP # default, can be omitted selector: { app: <label> } ports: - port: <port> targetPort: <containerPort>

ClusterIP is the default Service type. It gives your Pods a virtual IP that is reachable only from within the cluster — perfect for internal traffic between microservices.

When to use it

  • A backend API that only your frontend Pods call.
  • A database or cache that should never be exposed publicly.
  • Any service-to-service communication inside the cluster.

Reaching it

Other Pods connect using the Service's DNS name, typically just its name within the same namespace. No IP addresses to remember.

Example

Example · yaml
apiVersion: v1
kind: Service
metadata:
  name: backend
spec:
  type: ClusterIP
  selector:
    app: backend
  ports:
    - port: 8080
      targetPort: 8080
# Reach it from another Pod as: http://backend:8080

When to use it

  • A backend API Service is exposed as ClusterIP so only other pods inside the cluster can call it, preventing any external access.
  • A Redis cache is published as a ClusterIP Service so application pods can connect to redis-svc:6379 without knowing any pod IPs.
  • A headless ClusterIP Service (clusterIP: None) lets StatefulSet pods discover peer pods via DNS for peer-to-peer clustering.

More examples

ClusterIP Service for internal API

Creates a ClusterIP Service accessible only within the cluster at api-internal:8080, selecting all pods labelled app=api.

Example · yaml
apiVersion: v1
kind: Service
metadata:
  name: api-internal
spec:
  type: ClusterIP
  selector:
    app: api
  ports:
    - port: 8080
      targetPort: 8080

Test ClusterIP connectivity

Tests a ClusterIP Service from within the cluster using both the short name and the full DNS name across namespaces.

Example · bash
# From another pod in the same namespace
kubectl run curl --image=curlimages/curl --rm -it -- \
  curl http://api-internal:8080/health

# From a different namespace using FQDN
curl http://api-internal.default.svc.cluster.local:8080/health

Headless Service for StatefulSet

Sets clusterIP: None to create a headless Service that returns individual pod IPs via DNS, required by StatefulSets.

Example · yaml
apiVersion: v1
kind: Service
metadata:
  name: mysql-headless
spec:
  clusterIP: None
  selector:
    app: mysql
  ports:
    - port: 3306

Related

k8s services introk8s dns

Discussion

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