providers/aws: support non-destructive update of desired_capacity for

ASG

builtin/providers/aws/resource_aws_autoscaling_group.go

@@ -33,7 +33,6 @@ func resourceAwsAutoscalingGroup() *schema.Resource {
 				Type:     schema.TypeInt,
 				Optional: true,
 				Computed: true,
-				ForceNew: true,
 			},
 
 			"min_size": &schema.Schema{
@@ -168,6 +167,11 @@ func resourceAwsAutoscalingGroupUpdate(d *schema.ResourceData, meta interface{})
 		Name: d.Id(),
 	}
 
+	if d.HasChange("desired_capacity") {
+		opts.DesiredCapacity = d.Get("desired_capacity").(int)
+		opts.SetDesiredCapacity = true
+	}
+
 	if d.HasChange("min_size") {
 		opts.MinSize = d.Get("min_size").(int)
 		opts.SetMinSize = true

builtin/providers/aws/resource_aws_autoscaling_group_test.go

@@ -40,6 +40,15 @@ func TestAccAWSAutoScalingGroup_basic(t *testing.T) {
 						"aws_autoscaling_group.bar", "force_delete", "true"),
 				),
 			},
+
+			resource.TestStep{
+				Config: testAccAWSAutoScalingGroupConfigUpdate,
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckAWSAutoScalingGroupExists("aws_autoscaling_group.bar", &group),
+					resource.TestCheckResourceAttr(
+						"aws_autoscaling_group.bar", "desired_capacity", "5"),
+				),
+			},
 		},
 	})
 }
@@ -198,6 +207,27 @@ resource "aws_autoscaling_group" "bar" {
 }
 `
 
+const testAccAWSAutoScalingGroupConfigUpdate = `
+resource "aws_launch_configuration" "foobar" {
+  name = "foobarautoscaling-terraform-test"
+  image_id = "ami-21f78e11"
+  instance_type = "t1.micro"
+}
+
+resource "aws_autoscaling_group" "bar" {
+  availability_zones = ["us-west-2a"]
+  name = "foobar3-terraform-test"
+  max_size = 5
+  min_size = 2
+  health_check_grace_period = 300
+  health_check_type = "ELB"
+  desired_capacity = 5
+  force_delete = true
+
+  launch_configuration = "${aws_launch_configuration.foobar.name}"
+}
+`
+
 const testAccAWSAutoScalingGroupConfigWithLoadBalancer = `
 resource "aws_elb" "bar" {
   name = "foobar-terraform-test"