External data source for Terraform that provides tags for all images in an ECS task definition

data_source.tf

# Use current image versions to avoid surreptitious app deployments
data "external" "active_image_versions" {
  program = ["python", "/scripts/get_image_tags.py"]
 
  query = {
    cluster_name = "${data.terraform_remote_state.ecs.ecs_cluster_id}"
    service_name = "${var.app_name}"
  }
}