How to get default CIDR block for my EC2 instances with terraform?

Question

I'd like to create security group which allow me to communicate between instances within subnet and don't expose some ports outside. Of course I can explicite specify my CIDR, but how create data source which give me CIDR block for my subnet in default VPC?

Answer 1

with terraform data source aws_vpc, you can get what you need.

The example shows what you need.

variable "vpc_id" {}

data "aws_vpc" "selected" {
  id = "${var.vpc_id}"
}

resource "aws_subnet" "example" {
  vpc_id            = "${data.aws_vpc.selected.id}"
  availability_zone = "us-west-2a"
  cidr_block        = "${cidrsubnet(data.aws_vpc.selected.cidr_block, 4, 1)}"
}