From 4147c1ea2b51c2c6a6e414e32518518450e81a62 Mon Sep 17 00:00:00 2001
From: Joshua Spence <josh@freelancer.com>
Date: Thu, 20 Jul 2017 20:55:11 +1000
Subject: [PATCH] Suppress diffs when an empty set is specified for
 `aws_autoscaling_group.availability_zones`

Fixes #1187.
---
 aws/diff_suppress_funcs.go                 | 10 +++++
 aws/resource_aws_autoscaling_group.go      | 11 +++---
 aws/resource_aws_autoscaling_group_test.go | 45 ++++++++++++++++++++++
 3 files changed, 61 insertions(+), 5 deletions(-)

diff --git a/aws/diff_suppress_funcs.go b/aws/diff_suppress_funcs.go
index e8c58b81306..d891708b918 100644
--- a/aws/diff_suppress_funcs.go
+++ b/aws/diff_suppress_funcs.go
@@ -75,3 +75,13 @@ func suppressOpenIdURL(k, old, new string, d *schema.ResourceData) bool {
 
 	return oldUrl.String() == newUrl.String()
 }
+
+func suppressAutoscalingGroupAvailabilityZoneDiffs(k, old, new string, d *schema.ResourceData) bool {
+	// If VPC zone identifiers are provided then there is no need to explicitly
+	// specify availability zones.
+	if _, ok := d.GetOk("vpc_zone_identifier"); ok {
+		return true
+	}
+
+	return false
+}
diff --git a/aws/resource_aws_autoscaling_group.go b/aws/resource_aws_autoscaling_group.go
index e53de952395..a0455cfcf8d 100644
--- a/aws/resource_aws_autoscaling_group.go
+++ b/aws/resource_aws_autoscaling_group.go
@@ -113,11 +113,12 @@ func resourceAwsAutoscalingGroup() *schema.Resource {
 			},
 
 			"availability_zones": {
-				Type:     schema.TypeSet,
-				Optional: true,
-				Computed: true,
-				Elem:     &schema.Schema{Type: schema.TypeString},
-				Set:      schema.HashString,
+				Type:             schema.TypeSet,
+				Optional:         true,
+				Computed:         true,
+				Elem:             &schema.Schema{Type: schema.TypeString},
+				Set:              schema.HashString,
+				DiffSuppressFunc: suppressAutoscalingGroupAvailabilityZoneDiffs,
 			},
 
 			"placement_group": {
diff --git a/aws/resource_aws_autoscaling_group_test.go b/aws/resource_aws_autoscaling_group_test.go
index 46609211540..39b63efe97f 100644
--- a/aws/resource_aws_autoscaling_group_test.go
+++ b/aws/resource_aws_autoscaling_group_test.go
@@ -857,6 +857,26 @@ func TestAccAWSAutoScalingGroup_classicVpcZoneIdentifier(t *testing.T) {
 	})
 }
 
+func TestAccAWSAutoScalingGroup_emptyAvailabilityZones(t *testing.T) {
+	var group autoscaling.Group
+
+	resource.Test(t, resource.TestCase{
+		PreCheck:      func() { testAccPreCheck(t) },
+		IDRefreshName: "aws_autoscaling_group.test",
+		Providers:     testAccProviders,
+		CheckDestroy:  testAccCheckAWSAutoScalingGroupDestroy,
+		Steps: []resource.TestStep{
+			resource.TestStep{
+				Config: testAccAWSAutoScalingGroupConfig_emptyAvailabilityZones,
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckAWSAutoScalingGroupExists("aws_autoscaling_group.test", &group),
+					resource.TestCheckResourceAttr("aws_autoscaling_group.test", "availability_zones.#", "1"),
+				),
+			},
+		},
+	})
+}
+
 const testAccAWSAutoScalingGroupConfig_autoGeneratedName = `
 resource "aws_launch_configuration" "foobar" {
   image_id = "ami-21f78e11"
@@ -1826,3 +1846,28 @@ resource "aws_launch_configuration" "test" {
   instance_type = "t1.micro"
 }
 `
+
+const testAccAWSAutoScalingGroupConfig_emptyAvailabilityZones = `
+resource "aws_vpc" "test" {
+  cidr_block = "10.0.0.0/16"
+}
+
+resource "aws_subnet" "test" {
+  vpc_id     = "${aws_vpc.test.id}"
+  cidr_block = "10.0.0.0/16"
+}
+
+resource "aws_autoscaling_group" "test" {
+  min_size = 0
+  max_size = 0
+
+  availability_zones   = []
+  launch_configuration = "${aws_launch_configuration.test.name}"
+  vpc_zone_identifier  = ["${aws_subnet.test.id}"]
+}
+
+resource "aws_launch_configuration" "test" {
+  image_id      = "ami-21f78e11"
+  instance_type = "t1.micro"
+}
+`