r/aws_lb_target_group - when creating a new target group check that

there are no target groups with the same name

Fixes an issue where target groups with an identical configuration
could both point to the same ARN

.changelog/26976.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+resource/aws_lb_target_group: when creating a new target group check for an existing target group with the same name
+```

internal/service/elbv2/find.go

@@ -92,3 +92,19 @@ func FindTargetGroupByARN(conn *elbv2.ELBV2, arn string) (*elbv2.TargetGroup, er
 
 	return nil, nil
 }
+
+func FindTargetGroupByName(conn *elbv2.ELBV2, name string) (*elbv2.TargetGroup, error) {
+	output, err := conn.DescribeTargetGroups(&elbv2.DescribeTargetGroupsInput{
+		Names: aws.StringSlice([]string{name}),
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	if len(output.TargetGroups) == 0 {
+		return nil, nil
+	}
+
+	return output.TargetGroups[0], nil
+}

internal/service/elbv2/target_group.go

@@ -301,6 +301,14 @@ func resourceTargetGroupCreate(d *schema.ResourceData, meta interface{}) error {
 		groupName = resource.PrefixedUniqueId("tf-")
 	}
 
+	existingTg, err := FindTargetGroupByName(conn, groupName)
+	if err != nil && !tfawserr.ErrCodeEquals(err, elbv2.ErrCodeTargetGroupNotFoundException) {
+		return fmt.Errorf("finding target group by name (%s): %w", groupName, err)
+	}
+	if existingTg != nil {
+		return fmt.Errorf("target group with name (%s) already exists", groupName)
+	}
+
 	params := &elbv2.CreateTargetGroupInput{
 		Name:       aws.String(groupName),
 		TargetType: aws.String(d.Get("target_type").(string)),

internal/service/elbv2/target_group_test.go

@@ -2085,6 +2085,32 @@ func TestAccELBV2TargetGroup_ALBAlias_updateStickinessEnabled(t *testing.T) {
 	})
 }
 
+func TestAccELBV2TargetGroup_Name_noDuplicates(t *testing.T) {
+	var targetGroup elbv2.TargetGroup
+	tgName := sdkacctest.RandomWithPrefix(acctest.ResourcePrefix)
+	resourceName := "aws_lb_target_group.first"
+
+	resource.ParallelTest(t, resource.TestCase{
+		PreCheck:                 func() { acctest.PreCheck(t) },
+		ErrorCheck:               acctest.ErrorCheck(t, elbv2.EndpointsID),
+		ProtoV5ProviderFactories: acctest.ProtoV5ProviderFactories,
+		CheckDestroy:             testAccCheckTargetGroupDestroy,
+		Steps: []resource.TestStep{
+			{
+				Config: testAccTargetGroupConfig_duplicateNameFirst(tgName),
+				Check: resource.ComposeAggregateTestCheckFunc(
+					testAccCheckTargetGroupExists(resourceName, &targetGroup),
+					resource.TestCheckResourceAttr(resourceName, "name", tgName),
+				),
+			},
+			{
+				Config:      testAccTargetGroupConfig_duplicateNameFirstAndSecond(tgName),
+				ExpectError: regexp.MustCompile("target group with name (.*?) already exist"),
+			},
+		},
+	})
+}
+
 func testAccTargetGroupConfig_albDefaults(rName string) string {
 	return fmt.Sprintf(`
 resource "aws_lb_target_group" "test" {
@@ -3723,6 +3749,63 @@ resource "aws_vpc" "test" {
 }`, rName)
 }
 
+func testAccTargetGroupConfig_duplicateNameFirst(rName string) string {
+	return fmt.Sprintf(`
+resource "aws_lb_target_group" "first" {
+  name     = %[1]q
+  port     = 443
+  protocol = "HTTPS"
+  vpc_id   = aws_vpc.test.id
+
+  tags = {
+    Name = %[1]q
+  }
+}
+
+resource "aws_vpc" "test" {
+  cidr_block = "10.0.0.0/16"
+
+  tags = {
+    Name = %[1]q
+  }
+}
+`, rName)
+}
+
+func testAccTargetGroupConfig_duplicateNameFirstAndSecond(rName string) string {
+	return fmt.Sprintf(`
+resource "aws_lb_target_group" "first" {
+  name     = %[1]q
+  port     = 443
+  protocol = "HTTPS"
+  vpc_id   = aws_vpc.test.id
+
+  tags = {
+    Name = %[1]q
+  }
+}
+
+resource "aws_lb_target_group" "second" {
+  name     = %[1]q
+  port     = 443
+  protocol = "HTTPS"
+  vpc_id   = aws_vpc.test.id
+
+  tags = {
+    Name = %[1]q
+  }
+}
+
+resource "aws_vpc" "test" {
+  cidr_block = "10.0.0.0/16"
+
+  tags = {
+    Name = %[1]q
+  }
+}
+`, rName)
+}
+
 func testAccCheckATargetGroupDestroy(s *terraform.State) error {
 	conn := acctest.Provider.Meta().(*conns.AWSClient).ELBV2Conn