provider/aws: Expose ARN suffix on ALB

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 ""
+}

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))

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