variable "foo" { default = "bar"; description = "bar"; } provider "aws" { access_key = "foo"; secret_key = "bar"; } provider "do" { api_key = "${var.foo}"; } resource "aws_security_group" "firewall" { } resource aws_instance "web" { ami = "${var.foo}" security_groups = [ "foo", "${aws_security_group.firewall.foo}" ] }