Merge pull request kubernetes#1413 from aledbf/resolve-external-names

Validate external names

core/pkg/ingress/controller/controller.go

@@ -19,6 +19,7 @@ package controller
 import (
 	"fmt"
 	"math/rand"
+	"net"
 	"reflect"
 	"sort"
 	"strconv"
@@ -1090,6 +1091,14 @@ func (ic *GenericController) getEndpoints(
 			return upsServers
 		}
 
+		if net.ParseIP(s.Spec.ExternalName) == nil {
+			_, err := net.LookupHost(s.Spec.ExternalName)
+			if err != nil {
+				glog.Errorf("unexpected error resolving host %v: %v", s.Spec.ExternalName, err)
+				return upsServers
+			}
+		}
+
 		return append(upsServers, ingress.Endpoint{
 			Address:     s.Spec.ExternalName,
 			Port:        fmt.Sprintf("%v", targetPort),