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

you can use local_file with the list with more host vars

resource "local_file" "ansible_hosts" {
  count   = "${var.customer_plan == "micro" ? "1" : "0"}"

  content = "[fenodes]\n${join("\n",
            formatlist(
              "%s ansible_host=%s is_scheduler=true",
              profitbricks_server.fe.*.name,
              profitbricks_server.fe.*.primary_ip
            )
            )}\n\n[benodes]\n${join("\n",
            formatlist(
              "%s ansible_host=%s",
              profitbricks_server.be.*.name,
              profitbricks_server.be.*.primary_ip
            )
            )}\n\n[dbnodes]\n${join("\n",
            formatlist(
              "%s ansible_host=%s metrics_aggregator=true",
              profitbricks_server.db.*.name,
              profitbricks_server.db.*.primary_ip
            )
            )}\n\n[cachenodes]\n${join("\n",
            formatlist(
              "%s ansible_host=%s cache_role=master",
              profitbricks_server.db.*.name,
              profitbricks_server.db.*.primary_ip
            )
            )}\n\n[all:vars]\nansible_user=root\nansible_ssh_pass=${var.image_password}\nansible_private_key_file=configs/ssh/id_rsa\nansible_ssh_common_args='-o StrictHostKeyChecking=yes'"
  filename = "${var.customer_name}-${var.customer_env}-host"

}