Populate endpoints and allow ports with headless service

pkg/api/validation/validation.go

@@ -4012,13 +4012,11 @@ func validateEndpointSubsets(subsets []api.EndpointSubset, oldSubsets []api.Endp
 		ss := &subsets[i]
 		idxPath := fldPath.Index(i)
 
+		// EndpointSubsets must include endpoint address. For headless service, we allow its endpoints not to have ports.
 		if len(ss.Addresses) == 0 && len(ss.NotReadyAddresses) == 0 {
 			//TODO: consider adding a RequiredOneOf() error for this and similar cases
 			allErrs = append(allErrs, field.Required(idxPath, "must specify `addresses` or `notReadyAddresses`"))
 		}
-		if len(ss.Ports) == 0 {
-			allErrs = append(allErrs, field.Required(idxPath.Child("ports"), ""))
-		}
 		for addr := range ss.Addresses {
 			allErrs = append(allErrs, validateEndpointAddress(&ss.Addresses[addr], idxPath.Child("addresses").Index(addr), ipToNodeName)...)
 		}