why you no null

gistfile1.txt

resource "null_resource" "init_serf" {
  count = "${var.num_nodes}"

  depends_on = [ "digitalocean_droplet.serf" ]

  provisioner "remote-exec" {
	connection {
	  user = "root"
	}

	inline = [
	  "/opt/serf join ${digitalocean_droplet.serf.0.ipv4_address}"
	]
  }
}