Add retry to LookupHost used to check the content of ExternalName

internal/ingress/controller/endpoints.go

@@ -21,7 +21,9 @@ import (
 	"net"
 	"reflect"
 	"strconv"
+	"time"
 
+	"k8s.io/apimachinery/pkg/util/wait"
 	"k8s.io/klog"
 
 	corev1 "k8s.io/api/core/v1"
@@ -56,10 +58,28 @@ func getEndpoints(s *corev1.Service, port *corev1.ServicePort, proto corev1.Prot
 			return upsServers
 		}
 
+		// if the externalName is not an IP address we need to validate is a valid FQDN
 		if net.ParseIP(s.Spec.ExternalName) == nil {
-			_, err := net.LookupHost(s.Spec.ExternalName)
+			defaultRetry := wait.Backoff{
+				Steps:    2,
+				Duration: 1 * time.Second,
+				Factor:   1.5,
+				Jitter:   0.2,
+			}
+
+			var lastErr error
+			err := wait.ExponentialBackoff(defaultRetry, func() (bool, error) {
+				_, err := net.LookupHost(s.Spec.ExternalName)
+				if err == nil {
+					return true, nil
+				}
+
+				lastErr = err
+				return false, nil
+			})
+
 			if err != nil {
-				klog.Errorf("Error resolving host %q: %v", s.Spec.ExternalName, err)
+				klog.Errorf("Error resolving host %q: %v", s.Spec.ExternalName, lastErr)
 				return upsServers
 			}
 		}