Extend aws_lb_listener data resource to output target_group_arn

[e-moshaya]

I have two separate blue/green target groups. I would like to use data aws_lb_listener resource to output the active target_group_arn so I can figure out if we're in blue or green target group. I can already achieve this via the cli

aws elbv2 describe-listeners --listener-arns aws_lb_listener.service.arn --query 'Listeners[].DefaultActions[].TargetGroupArn' --output text

It would be great if terraform can support this too?

[nijave]

Looks like it already works

provider "aws" {}

data "aws_lb_listener" "test" {
  arn = "arn:aws:elasticloadbalancing:us-east-1:12345:listener/app/my-lb/54321/abc123"
}

output "target_group" {
  value = "${data.aws_lb_listener.test.default_action.1.target_group_arn}"
}

My ALB has another rule first so I used 1 instead of 0

terraform state show data.aws_lb_listener.test will show you what attributes are available

[e-moshaya]

@nijave I tried your output . target_group_arn didn't work. I got the following error:

Error: Unsupported attribute

  on ../../modules/aws-ecs-terraform-module/ecs_service.tf line 82, in resource "aws_ecs_service" "this":
  82:     target_group_arn = data.aws_lb_listener.this[0].target_group_arn

This object has no argument, nested block, or exported attribute named
"target_group_arn".