From 6e818785afd2b9134c2b338930f10eee0a4e9586 Mon Sep 17 00:00:00 2001
From: Clint Shryock <clint@ctshryock.com>
Date: Wed, 24 Jun 2015 16:37:23 -0500
Subject: [PATCH] provider/aws: Update ASGs to support in-place updates for
 Load Balancers

---
 .../aws/resource_aws_autoscaling_group.go     | 37 ++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/builtin/providers/aws/resource_aws_autoscaling_group.go b/builtin/providers/aws/resource_aws_autoscaling_group.go
index bf9b30c6a..abded26af 100644
--- a/builtin/providers/aws/resource_aws_autoscaling_group.go
+++ b/builtin/providers/aws/resource_aws_autoscaling_group.go
@@ -92,7 +92,6 @@ func resourceAwsAutoscalingGroup() *schema.Resource {
 			"load_balancers": &schema.Schema{
 				Type:     schema.TypeSet,
 				Optional: true,
-				ForceNew: true,
 				Elem:     &schema.Schema{Type: schema.TypeString},
 				Set:      schema.HashString,
 			},
@@ -258,6 +257,42 @@ func resourceAwsAutoscalingGroupUpdate(d *schema.ResourceData, meta interface{})
 		return fmt.Errorf("Error updating Autoscaling group: %s", err)
 	}
 
+	if d.HasChange("load_balancers") {
+
+		o, n := d.GetChange("load_balancers")
+		if o == nil {
+			o = new(schema.Set)
+		}
+		if n == nil {
+			n = new(schema.Set)
+		}
+
+		os := o.(*schema.Set)
+		ns := n.(*schema.Set)
+		remove := expandStringList(os.Difference(ns).List())
+		add := expandStringList(ns.Difference(os).List())
+
+		if len(remove) > 0 {
+			_, err := conn.DetachLoadBalancers(&autoscaling.DetachLoadBalancersInput{
+				AutoScalingGroupName: aws.String(d.Id()),
+				LoadBalancerNames:    remove,
+			})
+			if err != nil {
+				return fmt.Errorf("[WARN] Error updating Load Balancers for AutoScaling Group (%s), error: %s", d.Id(), err)
+			}
+		}
+
+		if len(add) > 0 {
+			_, err := conn.AttachLoadBalancers(&autoscaling.AttachLoadBalancersInput{
+				AutoScalingGroupName: aws.String(d.Id()),
+				LoadBalancerNames:    add,
+			})
+			if err != nil {
+				return fmt.Errorf("[WARN] Error updating Load Balancers for AutoScaling Group (%s), error: %s", d.Id(), err)
+			}
+		}
+	}
+
 	return resourceAwsAutoscalingGroupRead(d, meta)
 }