From 9d51ebd0aa8984f7e2aa518bdef22faad46a0936 Mon Sep 17 00:00:00 2001
From: James Nugent <james@jen20.com>
Date: Wed, 14 Sep 2016 15:50:10 +0100
Subject: [PATCH] provider/aws: Expose ARN suffix on ALB (#8833)

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 0668ed4af..da26ce49b 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 d6d5a48f8..168eda6c1 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 c4b258253..e69a92a87 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