Get load balancer ARN when using alb ingress controller

get-load-balancers-data.sh

#!/usr/bin/env bash

# Usage:
# echo '{"ingress_name": "my-ingress-name"}' | sh get-ingress-data.sh

set -o errexit
set -o nounset
set -o pipefail

function parse_input() {
  eval "$(jq -r '@sh "export ingress_name=\(.ingress_name)"')"
}

# Returns [{"arn": "", {"name": ""}}]
getLoadBalancers() {
  aws elbv2 describe-load-balancers |
    jq -r '[.LoadBalancers[] | {"arn": .LoadBalancerArn, "name": .LoadBalancerName}]'
}

# $1: [{"arn": "", "name": ""}]
# Returns ARNs separated by spaces
getAllARNs() {
  echo $1 |
    jq -r '.[] .arn' | tr '\n' ' '
}

# $1: ARNs separated by spaces
# $2: ingress name present in load balancer tags
# Returns [{"arn": "", "ingress_name": ""}]
getARNsByIngressNameInTag() {
  aws elbv2 describe-tags --resource-arns $1 |
    jq '.TagDescriptions' |
    jq '[.[] | {"arn": .ResourceArn, "ingress_name": .Tags[] | select(.Key ==
      "kubernetes.io/ingress-name") | .Value}]' |
    jq -r "[.[] | select( .ingress_name | contains(\"$2\"))]"
}

# $1: [{"arn": "", "name": ""}]
# $2: [{"arn": "", "ingress_name": ""}]
# Returns an object {"load_balancers": ""}. The return value needs to be a
# map[string]string (Terraform limitations), that's why we use tostring on the
# array of load balancers.
output() {
  # https://github.com/stedolan/jq/issues/1475
  jq -n \
    --argjson lbs "$1" \
    --argjson arns "$2" \
    '{lbs: $lbs, "arns": $arns}' |
    jq '{"load_balancers": [.lbs[] as $lb | (
      .arns[] | select(
        $lb.arn == .arn
      ) as $tmp | {
       "arn": $lb.arn,
       "name": $lb.name,
       "ingress_name": $tmp.ingress_name
      }
    )] | tostring}'
}

main() {
  parse_input
  loadBalancers=$(getLoadBalancers)
  allARNs=$(getAllARNs "$loadBalancers")
  ARNs=$(getARNsByIngressNameInTag "$allARNs" "$ingress_name")
  output "$loadBalancers" "$ARNs"
}
main

main.tf

data "external" ingress {
  program = ["sh", "${path.module}/get-load-balancers-data.sh"]
  query = {
    ingress_name = local.ingress_name
  }
  depends_on = [kubernetes_ingress.ingress]
}

locals {
  load_balancers = jsondecode(data.external.ingress.result["load_balancers"])
}

data "aws_lb" ingress {
  arn  = local.load_balancers[0].arn
  name = local.load_balancers[0].name
}