Why does terraform aws code fail to render? - bash

Question

Terraform version = 0.12
resource "aws_instance" "bespin-ec2-web" {
ami = "ami-0bea7fd38fabe821a"
instance_type = "t2.micro"
vpc_security_group_ids = [aws_security_group.bespin-sg.id]
subnet_id = aws_subnet.bespin-subnet-public-a.id
associate_public_ip_address = true
tags = {
Name = "bespin-ec2-web-a"
}
user_data = data.template_file.user_data.rendered
}
data "template_file" "user_data" {
template = file("${path.module}/userdata.sh")
}
userdata.sh file
#!/bin/bash
USERS="bespin"
GROUP="bespin"
for i in $USERS; do
/usr/sbin/adduser ${i};
/bin/echo ${i}:${i}1! | chpasswd;
done
cp -a /etc/ssh/sshd_config /etc/ssh/sshd_config_old
sed -i 's/PasswordAuthentication no/#PasswordAuthentication no/' /etc/ssh/sshd_config
sed -i 's/#PasswordAuthentication yes/PasswordAuthentication yes/' /etc/ssh/sshd_config
systemctl restart sshd
terraform plan result
Error: failed to render : <template_file>:5,24-25: Unknown variable; There is no variable named "i"., and 2 other di
agnostic(s)
on instance.tf line 13, in data "template_file" "user_data":
13: data "template_file" "user_data" {
Why am I getting an error?

Answer 1

The template argument in the template_file data source is processed as Terraform template syntax.
In this syntax, using ${...} has a special meaning, that the ... part will be injected by some var that is passed into the template.
Bash also allows this syntax, for getting the values of variables as you're intending to use it.
To reconcile this, you'll need to escape the $ character so that the terraform template compiler will leave it be, which you can do by doubling up the character: $${i} in all cases.
https://www.terraform.io/docs/configuration/expressions.html#string-templates