Deploying subnets in AZs automatically

[Francisco Javier Romero Mendiola]

I am trying to setting up subnets per AZs within regions. This is my aws_subnet resource:

resource "aws_subnet" "internal" {

  count                   = "${length(split(",", lookup(var.aws_azs, var.region)))}"

  vpc_id                  = "${aws_vpc.main.id}"

  cidr_block              = "${element(var.subnet_int_cidr, count.index)}"

  availability_zone       = "${element((lookup(var.aws_azs,var.region)),count.index)}"

  tags {

    Name    = "${var.subnet_int_name}${count.index + 1}"

  }

}

When I issue "terraform plan" it prints the following error:

$ terraform plan

Error configuring: 2 error(s) occurred:

* lookup: lookup() may only be used with flat maps, this map contains elements of type list in:

${length(split(",", lookup(var.aws_azs, var.region)))}

Could be this a new feature or there is another solution?

Regards.

[Francisco Javier Romero Mendiola]

I achieved if I declare a map with strings and not a map:

variable "aws_azs" {

  description = "AWS Availability Zones"

  default = {

    us-east-1     = "us-east-1a,us-east-1c,us-east-1d"

    eu-west-1     = "eu-west-1a,eu-west-1b,eu-west-1c"

    eu-central-1  = "eu-central-1a,eu-central-1b,eu-central-1c"

[Martin Atkins]

Hi Francisco,

In Terraform 0.7 it's suggested to use the square bracket indexing syntax rather than the element and lookup functions. The type system for functions in Terraform doesn't allow a function's return type to vary based on its input type, so the functions must always return strings.

var.subnet_int_cidr[count.index]

var.aws_azs[var.region]

Since this is a first-class operator in Terraform, it is able to vary on operand type as we need here, and so should achieve what you're looking for I believe.

[Francisco Javier Romero Mendiola]

Thanks for your response Martin.

Where can I find that information about square bracket indexing syntax?

Regards.

[Adam Gotterer]

I was working on something similar today. This is what I ended up with:

variable "private_subnets" {

  description "A list of private subnets"

  default = {

    us-east-1a = "10.0.0.0/19"

    us-east-1b = "10.0.32.0/19"

    us-east-1c = "10.0.64.0/19"

  }

}

resource "aws_subnet" "private" {

  vpc_id = "${aws_vpc.default.id}"

  cidr_block = "${lookup(var.private_subnets, element(keys(var.private_subnets), count.index))}"

  availability_zone = "${element(keys(var.private_subnets), count.index)}"

  count = "${length(keys(var.private_subnets))}"

  tags {

    Name = "${var.name}: ${element(keys(var.private_subnets), count.index)} (private)"

  }

}

Hope that helps!

Adam