Best Practices: cout and count.index

This blog post demonstrates a sample Terraform configuration for AWS, including VPC and subnet resources with dynamic CIDR blocks and availability zones to determines cout and count.index.

Variables

variable "cidr_block" {
  type    = string
  default = "10.0.0.0/16"
}

variable "common_tags" {
  type = map(any)
  default = {
    Terraform   = "True"
    Environment = "Dev"
  }
}

variable "subnet_cidr" {
  type    = list(string)
  default = ["10.0.1.0/24", "10.0.11.0/24"]
}

variable "az" {
    type = list
    default = ["ap-south-1a","ap-south-1b"]
}

variable "subnet_names" {
    type = list(string)
    default = [ "GS Pub Subnet", "Gs Pvt Subnet" ]
}
    

AWS VPC Resource

resource "aws_vpc" "gs-vpc" {
  cidr_block       = var.cidr_block
  instance_tenancy = "default"
  tags = merge(
    {
      Name = "GS VPC"
    },
    var.common_tags
  )
}
    

AWS Subnet Resources

resource "aws_subnet" "gs-pub-1a" {
  vpc_id     = aws_vpc.gs-vpc.id
  count      = length(var.subnet_cidr)
  cidr_block = var.subnet_cidr[count.index]
  availability_zone = var.az[count.index]
  tags = merge(
    {
        Name = var.subnet_names[count.index]
    },
    var.common_tags
  )
}
    

The provided Terraform configuration sets up a VPC and subnets in multiple availability zones. The subnets' CIDR blocks and names are dynamically determined using lists, which are a common practice for managing multiple environments or regions.