From 339919db8317fde9aaa6a404ffceb995a7468503 Mon Sep 17 00:00:00 2001
From: James Nugent <james@jen20.com>
Date: Wed, 14 Sep 2016 09:42:52 +0100
Subject: [PATCH] provider/aws: Expose ARN suffix on ALB

When creating a CloudWatch Metric for an Application Load Balancer it is
neccessary to use the suffix of the ARN as the reference to the load
balancer. This commit exposes that as an attribute on the `aws_alb`
resource to prevent the need to use regular expression substitution to
make the reference.

Fixes #8808.
---
 builtin/providers/aws/resource_aws_alb.go     | 21 +++++++++++++
 .../providers/aws/resource_aws_alb_test.go    | 31 +++++++++++++++++++
 .../docs/providers/aws/r/alb.html.markdown    |  9 +++---
 3 files changed, 57 insertions(+), 4 deletions(-)

diff --git a/builtin/providers/aws/resource_aws_alb.go b/builtin/providers/aws/resource_aws_alb.go
index 0668ed4af6ce..da26ce49ba26 100644
--- a/builtin/providers/aws/resource_aws_alb.go
+++ b/builtin/providers/aws/resource_aws_alb.go
@@ -3,6 +3,7 @@ package aws
 import (
 	"fmt"
 	"log"
+	"regexp"
 	"strconv"
 
 	"github.com/aws/aws-sdk-go/aws"
@@ -28,6 +29,11 @@ func resourceAwsAlb() *schema.Resource {
 				Computed: true,
 			},
 
+			"arn_suffix": {
+				Type:     schema.TypeString,
+				Computed: true,
+			},
+
 			"name": {
 				Type:          schema.TypeString,
 				Optional:      true,
@@ -191,6 +197,7 @@ func resourceAwsAlbRead(d *schema.ResourceData, meta interface{}) error {
 	alb := describeResp.LoadBalancers[0]
 
 	d.Set("arn", alb.LoadBalancerArn)
+	d.Set("arn_suffix", albSuffixFromARN(alb.LoadBalancerArn))
 	d.Set("name", alb.LoadBalancerName)
 	d.Set("internal", (alb.Scheme != nil && *alb.Scheme == "internal"))
 	d.Set("security_groups", flattenStringList(alb.SecurityGroups))
@@ -345,3 +352,17 @@ func flattenSubnetsFromAvailabilityZones(availabilityZones []*elbv2.Availability
 	}
 	return result
 }
+
+func albSuffixFromARN(arn *string) string {
+	if arn == nil {
+		return ""
+	}
+
+	if arnComponents := regexp.MustCompile(`arn:.*:loadbalancer/(.*)`).FindAllStringSubmatch(*arn, -1); len(arnComponents) == 1 {
+		if len(arnComponents[0]) == 2 {
+			return arnComponents[0][1]
+		}
+	}
+
+	return ""
+}
diff --git a/builtin/providers/aws/resource_aws_alb_test.go b/builtin/providers/aws/resource_aws_alb_test.go
index d6d5a48f8e01..168eda6c1aeb 100644
--- a/builtin/providers/aws/resource_aws_alb_test.go
+++ b/builtin/providers/aws/resource_aws_alb_test.go
@@ -14,6 +14,37 @@ import (
 	"github.com/hashicorp/terraform/terraform"
 )
 
+func TestALBCloudwatchSuffixFromARN(t *testing.T) {
+	cases := []struct {
+		name   string
+		arn    *string
+		suffix string
+	}{
+		{
+			name:   "valid suffix",
+			arn:    aws.String(`arn:aws:elasticloadbalancing:us-east-1:123456:loadbalancer/app/my-alb/abc123`),
+			suffix: `app/my-alb/abc123`,
+		},
+		{
+			name:   "no suffix",
+			arn:    aws.String(`arn:aws:elasticloadbalancing:us-east-1:123456:loadbalancer`),
+			suffix: ``,
+		},
+		{
+			name:   "nil ARN",
+			arn:    nil,
+			suffix: ``,
+		},
+	}
+
+	for _, tc := range cases {
+		actual := albSuffixFromARN(tc.arn)
+		if actual != tc.suffix {
+			t.Fatalf("bad suffix: %q\nExpected: %s\n     Got: %s", tc.name, tc.suffix, actual)
+		}
+	}
+}
+
 func TestAccAWSALB_basic(t *testing.T) {
 	var conf elbv2.LoadBalancer
 	albName := fmt.Sprintf("testaccawsalb-basic-%s", acctest.RandStringFromCharSet(10, acctest.CharSetAlphaNum))
diff --git a/website/source/docs/providers/aws/r/alb.html.markdown b/website/source/docs/providers/aws/r/alb.html.markdown
index c4b25825377d..e69a92a8727f 100644
--- a/website/source/docs/providers/aws/r/alb.html.markdown
+++ b/website/source/docs/providers/aws/r/alb.html.markdown
@@ -59,11 +59,12 @@ Access Logs (`access_logs`) support the following:
 
 The following attributes are exported in addition to the arguments listed above:
 
-* `id` - The ARN of the load balancer (matches `arn`)
-* `arn` - The ARN of the load balancer (matches `id`)
-* `dns_name` - The DNS name of the load balancer
+* `id` - The ARN of the load balancer (matches `arn`).
+* `arn` - The ARN of the load balancer (matches `id`).
+* `arn_suffix` - The ARN suffix for use with CloudWatch Metrics.
+* `dns_name` - The DNS name of the load balancer.
 * `canonical_hosted_zone_id` - The canonical hosted zone ID of the load balancer.
-* `zone_id` - The canonical hosted zone ID of the load balancer (to be used in a Route 53 Alias record)
+* `zone_id` - The canonical hosted zone ID of the load balancer (to be used in a Route 53 Alias record).
 
 ## Import