Terraform - Use external data source to get EC2 instances count from AutoScaling Group and add EC2 IP to DNS records

consul.tf

data "external" "asg_cousul_count" {
  program = [
    "/bin/bash",
    "scripts/get_asg_instance_count.sh",
  ]

  query = {
    region         = "us-west-2"
    asg_group_name = "asg-consul-production"
  }
}

data "aws_instances" "asg_consul_production" {
  count = "${data.external.asg_cousul_count.result["count"] == "0" ? 0 : 1}"

  instance_tags {
    Name = "asg-consul-production"
  }

  instance_state_names = ["running"]
}

# use multi-answer DNS for asg
resource "aws_route53_record" "consul-server-dns-asg" {
  depends_on                       = ["data.aws_instances.asg_consul_production"]
  count                            = "${data.external.asg_cousul_count.result["count"]}"
  zone_id                          = "XXXXXXXXXXXX"
  name                             = "consul-server.service"
  type                             = "A"
  ttl                              = "300"
  allow_overwrite                  = true
  multivalue_answer_routing_policy = true
  set_identifier                   = "route to consul-server asg ${format("%03d", count.index + 1)}"
  records                          = ["${data.aws_instances.asg_consul_production.private_ips[count.index]}"]
}

get_asg_instance_count.sh

#!/bin/bash

set -e

eval "$(jq -r '@sh "export ASG_GROUP_NAME=\(.asg_group_name) REGION=\(.region)"')"

instance_ids=`aws autoscaling describe-auto-scaling-instances \
--region "${REGION}" --output text \
--query "AutoScalingInstances[?AutoScalingGroupName=='"${ASG_GROUP_NAME}"'].InstanceId"`

if [[ -z "${instance_ids}" ]]
then
    instance_count=0
else
    instance_count=`aws ec2 describe-instances --region "${REGION}" --instance-ids \
$(aws autoscaling describe-auto-scaling-instances --region "${REGION}" --output text \
--query "AutoScalingInstances[?AutoScalingGroupName=='"${ASG_GROUP_NAME}"'].InstanceId") \
--query "Reservations[].Instances[].PrivateIpAddress" | jq '. | length'`
fi

jq -n --arg count "$instance_count" '{"count":$count}'