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Terraform/AWS – Call to function "element" failed: cannot read elements from string

November 13, 2023

I am trying to deploy the following resource while cycling through my subnets.

resource "aws_subnet" "public" {
  vpc_id                   = aws_vpc.main.id
  cidr_block               = element(var.public_subnets_cidr, count.index)
  availability_zone        = element(var.`your text`availability_zones_public, count.index)
  count                    = length(var.public_subnets_cidr)

However, I’m receiving the following error.

│ Error: Error in function call

│ on vpc/main.tf line 33, in resource "aws_subnet" "private":

│ 33: cidr_block = element(var.private_subnets_cidr, count.index)

│ │ while calling element(list, index)

│ │ count.index is 30

││ var.private_subnets_cidr is "[\"192.168.4.0/24\",\"192.168.5.0/24\",\"192.168.6.0/24\"]"

│ Call to function "element" failed: cannot read elements from string.`

Any idea why this is? From the look of things, this should be fine?

    public_subnets_cidr          =  ["192.168.0.0/24", "192.168.1.0/24", "192.168.2.0/24"]
    private_subnets_cidr         =  ["192.168.4.0/24", "192.168.5.0/24", "192.168.6.0/24"]
    availability_zones_public    =  ["us-east-1a", "us-east-1b", "us-east-1c"]
    availability_zones_private   =  ["us-east-1d", "us-east-1b", "us-east-1f"]

>Solution :

The error is clear, var.private_subnets_cidr is "[\"192.168.4.0/24\",\"192.168.5.0/24\",\"192.168.6.0/24\"]" which is literal string, not a list ["192.168.4.0/24", "192.168.5.0/24", "192.168.6.0/24"].

You have to check your variables, probably you are overwriting private_subnets_cidr somewhere. Make sure you use a list, not a string as value for private_subnets_cidr.