Terraform > Unescaped interpolations - terraform

Question

What does this mean:
Note: Inline templates must escape their interpolations (as seen by the double
$ above). Unescaped interpolations will be processed before the template.
from https://www.terraform.io/docs/providers/template/index.html
The specific example is:
# Template for initial configuration bash script
data "template_file" "init" {
template = "$${consul_address}:1234"
vars {
consul_address = "${aws_instance.consul.private_ip}"
}
}

Answer 1

The ${} syntax is used by HCL for interpolation before the template rendering happens so if you were to just use:
# Template for initial configuration bash script
data "template_file" "init" {
template = "${consul_address}:1234"
vars {
consul_address = "${aws_instance.consul.private_ip}"
}
}
Terraform will attempt to find consul_address to template into the output instead of using the template variable of consul_address (which in turn is resolved to the private_ip output of the aws_instance.consul resource.
This is only an issue for inline templates and you don't need to do this for file based templates. For example this would be fine:
int.tpl
#!/bin/bash
echo ${consul_address}
template.tf
# Template for initial configuration bash script
data "template_file" "init" {
template = "${file("init.tpl")}"
vars {
consul_address = "${aws_instance.consul.private_ip}"
}
}
Of course if you then also needed to use the ${} syntax literally in your output template then you would need to double escape with something like this:
#!/bin/bash
CONSUL_ADDRESS_VAR=${consul_address}
echo $${CONSUL_ADDRESS_VAR}
This would then be rendered as:
#!/bin/bash
CONSUL_ADDRESS_VAR=1.2.3.4
echo ${CONSUL_ADDRESS_VAR}