Terraform lookup AWS region

Question

I have the following code in my main.tf file:

provider "aws" {
  access_key = "${var.aws_access_key}"
  secret_key = "${var.aws_secret_key}"
  region     = "us-east-1"
  alias      = "us-east-1"
}

provider "aws" {
  access_key = "${var.aws_access_key}"
  secret_key = "${var.aws_secret_key}"
  region     = "us-west-1"
  alias      = "us-west-1"
}

module "us-east_vpc" {
  source = "./setup-networking"

  providers = {
    "aws.region" = "aws.us-east-1"
  }
}

module "us-west_vpc" {
  source = "./setup-networking"

  providers = {
    "aws.region" = "aws.us-west-1"
  }
}

And then in my modules file I have:

provider "aws" {
  alias = "region"
}

resource "aws_vpc" "default" {
  provider             = "aws.region"
  cidr_block           = "${lookup(var.vpc_cidr, ${aws.region.region})}"
  enable_dns_hostnames = true

  tags {
    Name = "AWS VPC"
  }
}

resource "aws_internet_gateway" "default" {
  provider = "aws.region"
  vpc_id   = "${aws_vpc.default.id}"
}

resource "aws_subnet" "default" {
  provider = "aws.region"
  vpc_id   = "${aws_vpc.default.id}"

  cidr_block        = "${lookup(var.subnet_cidr, ${aws.region.region})}"
  availability_zone = "aws.region"

  tags {
    Name = "AWS Subnet"
  }
}

resource "aws_route_table" "default" {
  provider = "aws.region"
  vpc_id   = "${aws_vpc.default.id}"

  route {
    cidr_block = "0.0.0.0/0"
    gateway_id = "${aws_internet_gateway.default.id}"
  }

  tags {
    Name = "Main Gateway"
  }
}

As you can see in the modules file code I am trying to do a lookup to find the VPC CIDR mask and the subnet CIDR mask from map variables.

The trouble is that I can't seem to sort out how to get the region to be used as a lookup value.

If I hard code these values:

cidr_block = "10.10.0.0/16"
cidr_block = "10.10.10.0/24"

The script works as expected but I don't want to hard code the values.

Can someone with more Terraform experience help me understand how I can properly reference the region to lookup the correct value?

Answer 1

I was looking for the same answer for a different problem. I wanted to get the region for a name of a role, I was able to get the info by doing this:

1.- Create a file like data.tf and add this info:

data "aws_region" "current" {}

2.- Get the info from the data by calling this variable in any TF file:

name = "${var.vpc-name}-${data.aws_region.current.name}-Bastion-Role"

This way it will get the region where you are executing the code, and you don't have to mess with the provider.tf file.

Answer 2

You can get the region that's currently in use by the provider by using the aws_region data source.

So in your case you could do something like this:

provider "aws" {
  alias = "region"
}

data "aws_region" "current" {
  provider = "aws.region"
}

resource "aws_vpc" "default" {
  provider             = "aws.region"
  cidr_block           = "${lookup(var.vpc_cidr, ${data.aws_region.current.name})}"
  enable_dns_hostnames = true

  tags {
    Name = "AWS VPC"
  }
}

...