plugin/kubernetes: Create records for portless services (#2052)

inject sentinels for portless services

plugin/backend_lookup.go

@@ -172,6 +172,11 @@ func SRV(b ServiceBackend, zone string, state request.Request, opt Options) (rec
 		w[serv.Priority] += weight
 	}
 	for _, serv := range services {
+		// Don't add the entry if the port is -1 (invalid). The kubernetes plugin uses port -1 when a service/endpoint
+		// does not have any declared ports.
+		if serv.Port == -1 {
+			continue
+		}
 		w1 := 100.0 / float64(w[serv.Priority])
 		if serv.Weight == 0 {
 			w1 *= 100