Implement ability to update Load Balancer subnets

hack/.packages

@@ -160,6 +160,7 @@ k8s.io/kops/upup/pkg/kutil
 k8s.io/kops/upup/tools/generators/fitask
 k8s.io/kops/upup/tools/generators/pkg/codegen
 k8s.io/kops/util/pkg/hashing
+k8s.io/kops/util/pkg/slice
 k8s.io/kops/util/pkg/tables
 k8s.io/kops/util/pkg/ui
 k8s.io/kops/util/pkg/vfs

upup/pkg/fi/cloudup/awstasks/load_balancer.go

@@ -31,6 +31,7 @@ import (
 	"k8s.io/kops/upup/pkg/fi/cloudup/awsup"
 	"k8s.io/kops/upup/pkg/fi/cloudup/cloudformation"
 	"k8s.io/kops/upup/pkg/fi/cloudup/terraform"
+	"k8s.io/kops/util/pkg/slice"
 )
 
 // LoadBalancer manages an ELB.  We find the existing ELB using the Name tag.
@@ -527,7 +528,29 @@ func (_ *LoadBalancer) RenderAWS(t *awsup.AWSAPITarget, a, e, changes *LoadBalan
 				actualSubnets = append(actualSubnets, fi.StringValue(s.ID))
 			}
 
-			return fmt.Errorf("subnet changes on LoadBalancer not yet implemented: actual=%s -> expected=%s", actualSubnets, expectedSubnets)
+			oldSubnetIDs := slice.GetUniqueStrings(expectedSubnets, actualSubnets)
+			if len(oldSubnetIDs) > 0 {
+				request := &elb.DetachLoadBalancerFromSubnetsInput{}
+				request.SetLoadBalancerName(loadBalancerName)
+				request.SetSubnets(aws.StringSlice(oldSubnetIDs))
+
+				glog.V(2).Infof("Detaching Load Balancer from old subnets")
+				if _, err := t.Cloud.ELB().DetachLoadBalancerFromSubnets(request); err != nil {
+					return fmt.Errorf("Error detaching Load Balancer from old subnets: %v", err)
+				}
+			}
+
+			newSubnetIDs := slice.GetUniqueStrings(actualSubnets, expectedSubnets)
+			if len(newSubnetIDs) > 0 {
+				request := &elb.AttachLoadBalancerToSubnetsInput{}
+				request.SetLoadBalancerName(loadBalancerName)
+				request.SetSubnets(aws.StringSlice(newSubnetIDs))
+
+				glog.V(2).Infof("Attaching Load Balancer to new subnets")
+				if _, err := t.Cloud.ELB().AttachLoadBalancerToSubnets(request); err != nil {
+					return fmt.Errorf("Error attaching Load Balancer to new subnets: %v", err)
+				}
+			}
 		}
 
 		if changes.Listeners != nil {

util/pkg/slice/slice.go

@@ -0,0 +1,40 @@
+/*
+Copyright 2018 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package slice provides utility methods for common operations on slices.
+package slice
+
+// GetUniqueStrings returns a slice of strings in the extra slice that are not
+// present in the main slice
+func GetUniqueStrings(main, extra []string) []string {
+	unique := []string{}
+
+	for _, item := range extra {
+		found := false
+
+		for _, s := range main {
+			if item == s {
+				found = true
+			}
+		}
+
+		if !found {
+			unique = append(unique, item)
+		}
+	}
+
+	return unique
+}