ClusterIP Services
ClusterIP is the default Service type, reachable only from inside the cluster.
Syntax
spec:
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
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:8080When 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.
apiVersion: v1
kind: Service
metadata:
name: api-internal
spec:
type: ClusterIP
selector:
app: api
ports:
- port: 8080
targetPort: 8080Test ClusterIP connectivity
Tests a ClusterIP Service from within the cluster using both the short name and the full DNS name across namespaces.
# 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/healthHeadless Service for StatefulSet
Sets clusterIP: None to create a headless Service that returns individual pod IPs via DNS, required by StatefulSets.
apiVersion: v1
kind: Service
metadata:
name: mysql-headless
spec:
clusterIP: None
selector:
app: mysql
ports:
- port: 3306
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