Produce an Ansible inventory from a Terraform template

inventory.tf

data "template_file" "inventory" {
    template = "${file("inventory.tpl")}"

    vars {
        backend_ip = "${aws_instance.backend.public_ip}"
        frontend_ip = "${aws_instance.frontend.public_ip}"
        landing_ip = "${aws_instance.landing.public_ip}"
        key_path = "${var.instance_key_path}"
    }
}

resource "null_resource" "update_inventory" {

    triggers {
        template = "${data.template_file.inventory.rendered}"
    }

    provisioner "local-exec" {
        command = "echo '${data.template_file.inventory.rendered}' > ../inventory"
    }
}

inventory.tpl

[backend]
${backend_ip}

[frontend]
${frontend_ip}

[landing]
${landing_ip}

[all:vars]
ansible_ssh_private_key_file = ${key_path}
ansible_ssh_user = ubuntu