Terraform.tfvars parsing lists for variables.tf file - amazon-web-services

Question

I've got a couple of variables set in my variables.tf files which are of type list and I am trying to find the correct syntax on my .tfvars file
variables.tf
variable "subnet_cidrs" {
type = list(string)
description = "A list of Subnets CIDR's - Should consist of minimum 2"
}
variable "aws_region" {
type = string
description = "Region where all AWS Resources will be created"
}
variable "az" {
type = list(string)
description = "Availability-Zones - Should match numbers of CIDRs given and AWS Region"
}
terraform.tfvars
subnet_cidrs = ["192.168.1.100", "192.168.4.100"]
aws_region = "eu-central-1"
az = ["eu-central-1a", "eu-central-1b"]
A typical output i'll receive is :
│ Error: Incorrect attribute value type
│
│ on ..\ec2\ec2.tf line 21, in resource "aws_subnet" "public":
│ 21: availability_zone = var.az
│ ├────────────────
│ │ var.az is a list of dynamic
│
│ Inappropriate value for attribute "availability_zone": string required.
When brackets are removed for example : az = "eu-central-1a", "eu-central-1b"
It will return the following instead Argument definitions must be separated by newlines, not commas. An argument definition must end with a newline.
Edit
ec2.tf
I've made this as short as possible and included only the variables
# Main VPC
resource "aws_vpc" "main" {
cidr_block = var.vpc_cidr
tags = {
Name = "vpc-${var.name_prefix}"
}
}
# Two Subnets in different AZ - Public IP on launch
resource "aws_subnet" "public" {
count = length(var.subnet_cidrs)
cidr_block = var.subnet_cidrs
availability_zone = var.az
tags = {
Name = "subnet-${var.name_prefix}-${count.index}"
}
}
resource "aws_security_group" "ec2_sg" {
name = var.ec2_name
...
tags = {
Name = "EC2-SG-${var.name_prefix}"
}
}
# VM Key pair
resource "aws_key_pair" "auth" {
key_name = var.key_pair_name
public_key = file("~/.ssh/${var.ssh_file_name}.pub")
}
# EC2 Instance within 2 AZ's
resource "aws_instance" "ec2" {
count = length(var.subnet_cidrs)
tags = {
Name = "ubuntu-${var.name_prefix}-${count.index}"
}
}

Answer 1

Based on the variable definition and the way subnet resource is created, the following change is required:
resource "aws_subnet" "public" {
count = length(var.subnet_cidrs)
cidr_block = var.subnet_cidrs
availability_zone = var.az[count.index] # <---- using count.index here
tags = {
Name = "subnet-${var.name_prefix}-${count.index}"
}
}
This is needed because otherwise the problem will occur as availability_zone requires a single string value and passing only var.az will be an entire list. Using the count.index with the var.az will fetch a single value as is required.