A headless Service is created by setting spec.clusterIP: None, so B is correct. Normally, a Service gets a ClusterIP, and kube-proxy (or an alternative dataplane) implements virtual-IP-based load balancing to route traffic from that ClusterIP to the backend Pods. A headless Service intentionally disables that virtual IP allocation. Instead of giving you a single stable VIP, Kubernetes publishes DNS records that resolve directly to the endpoints (the Pod IPs) behind the Service.
This is especially important for workloads that need direct endpoint discovery or stable per-Pod identities, such as StatefulSets. With a headless Service, clients can discover all Pod IPs (or individual Pod DNS names in StatefulSet patterns) and implement their own selection, quorum, or leader/follower logic. Kubernetes DNS (CoreDNS) responds differently for headless Services: rather than returning a single ClusterIP, it returns multiple A/AAAA records (one per endpoint) or SRV records for named ports, enabling richer service discovery behavior.
The other options are invalid. “headless” is not a magic value for clusterIP; the API expects either an actual IP address assigned by the cluster or the special literal None. 0.0.0.0 and localhost are not valid ways to request headless semantics. Kubernetes uses None specifically to signal “do not allocate a ClusterIP.”
Operationally, headless Services are used to: (1) expose each backend instance individually, (2) support stateful clustering and stable DNS names, and (3) avoid load balancing when the application or client library must choose endpoints itself. The key is that the Service still provides a stable DNS name, but the resolution yields endpoints, not a VIP.
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