clusterIP

ClusterIP is the default Service type in Kubernetes that provides a stable virtual IP address (the Cluster IP) inside a cluster. It enables access to a set of pods chosen by a label selector through that internal IP, without exposing the service to external networks. Clients within the cluster can reach the service using the virtual IP or the standard DNS name for the service.

When a ClusterIP service is created, Kubernetes creates a Service object and an Endpoints object based on the selector. The kube-proxy on each node configures networking rules (iptables or IPVS) to load balance traffic addressed to the ClusterIP across the Pod IPs that match the selector.

The service is discoverable inside the cluster via DNS: serviceName.namespace.svc.cluster.local, or via its short name within the same namespace. This enables stable addressing even as pod IPs change.

A ClusterIP service defines a port and a targetPort. The port is the service port exposed to clients within the cluster, while targetPort is the port on the pods. Protocols are typically TCP, but UDP is supported as well. SessionAffinity can be configured, with the default being none.

By default, ClusterIP services are accessible only within the cluster. To expose the service externally, you can create a NodePort or a LoadBalancer service, or front it with an Ingress, depending on the cluster provider.

You manage ClusterIP services with standard YAML manifests that specify metadata, spec.selector, spec.ports, and optionally spec.clusterIP, which may be assigned automatically or set explicitly.