terraform_module_for_dynamic-subnet_creation

About

This is a Terraform Module used for creating Dynamic subnets ( both Public and Private ), the module itself will create and configure vpc, subnets, route table, Network ACLs etc. The module will do the ip-subnet calculations too.

Input Data Required

• Number of Public Subnets
• Number of Private Subnets ( if the value is 0 the module will not create NAT Gateway, Elastic IP and the routes associated with it )
• CIDR-Block
• Project Name

To use the Module

•  git clone https://github.com/ManuGeorge96/terraform_VPC_module_for_dynamic-subnet_creation.git

• Add below Module block on the main terraform code, replace source with correct value.

   module "vpc" {
     source = "PATH-TO-THE-MODULE/terraform_VPC_module_for_dynamic-subnet_creation"
     project = var.project
     Public-Count = var.Public_Count
     Private-Count = var.Private_Count
     cidr = var.cidr_vpc
   }

• Include below variables on your variable.tf,
  • project
  • Public_Count
  • Private_Count
  • cidr_vpc
• To get the Public Subnet ID's use,

  •  module.vpc.Public-Subnet-IDs

• To get the Private Subnet ID's use,

  •  module.vpc.Private-Subnet-IDs

• To get VPC ID use,

  •   module.vpc.VPC_ID

Behind The Code

• SECTION - 1
  • VPC Creation.

     resource "aws_vpc" "vpc-requestor" {
     cidr_block = var.cidr
     enable_dns_hostnames = true
     tags = {
       Name = "${var.project}-vpc"
       Project = "${var.project}"
      }
    }

• SECTION - 2
  • Calculates the new-bit for the CIDR Block.

     locals {
     subnetr = floor(log((var.Public-Count + var.Private-Count) * 2,2))
     }

  • Creation of Public Subnets.

     resource "aws_subnet" "requestor-Public" {
        cidr_block = cidrsubnet(var.cidr, local.subnetr, "${count.index}")
        availability_zone = element(data.aws_availability_zones.AZ-requestor.names, count.index)
        vpc_id = aws_vpc.vpc-requestor.id
        map_public_ip_on_launch = true
        count = var.Public-Count
         }

  • Creation of Private Subnets

      resource "aws_subnet" "requestor-Private" {
      count = var.Private-Count
      cidr_block = cidrsubnet(var.cidr, local.subnetr, "${count.index + var.Public-Count}")
      availability_zone = element(data.aws_availability_zones.AZ-requestor.names, count.index)
      vpc_id = aws_vpc.vpc-requestor.id
      map_public_ip_on_launch = false
       }  

• SECTION - 3
  • Creation of Elastic IP, creates only if there is private subnets,

      resource "aws_eip" "requestor-eip" {
        vpc = true
        count = var.Private-Count == "0" ? 0 : 1
      }

• SECTION - 4
  • Ctreation of NAT Gateway , creates only if there is private subnets,

     resource "aws_nat_gateway" "requestor-NAT" {
       count = var.Private-Count == "0" ? 0 : 1
       allocation_id = aws_eip.requestor-eip[0].id
       subnet_id = aws_subnet.requestor-Public[0].id
      }

• SECTION - 5
  • Creation of Internet Gateway.

      resource "aws_internet_gateway" "requestor-IGw" {
        vpc_id = aws_vpc.vpc-requestor.id
      }

• SECTION - 6
  • Public Route Table Creation

      resource "aws_route_table" "requestor-Public-RTB" {
        vpc_id = aws_vpc.vpc-requestor.id
        route {
          cidr_block = "0.0.0.0/0"
          gateway_id = aws_internet_gateway.requestor-IGw.id
        }
       }

  • Private Route Table Creation, creates only if there is private subnets

      resource "aws_route_table" "requestor-Private-RTB" {
        count = var.Private-Count == "0" ? 0 : 1
        vpc_id = aws_vpc.vpc-requestor.id
        route {
          cidr_block = "0.0.0.0/0"
          nat_gateway_id = aws_nat_gateway.requestor-NAT[0].id
        }
       }

• SECTION - 7
  • Route Table Assosciation for both Public and Private,

      resource "aws_route_table_association" "requestor-public" {
        count = "${length(aws_subnet.requestor-Public.*.cidr_block)}"
        subnet_id = "${element(aws_subnet.requestor-Public.*.id, count.index)}"
        route_table_id = aws_route_table.requestor-Public-RTB.id
      }
      resource "aws_route_table_association" "requestor-private" {
        count = "${length(aws_subnet.requestor-Private.*.cidr_block)}"
        subnet_id = "${element(aws_subnet.requestor-Private.*.id, count.index)}"
        route_table_id = aws_route_table.requestor-Private-RTB[0].id
      }

• SECTION - 8
  • Network ACL for both public and private witsh association,

      resource "aws_network_acl" "public" {
         vpc_id     = aws_vpc.vpc-requestor.id
         subnet_ids = aws_subnet.requestor-Public.*.id
         egress {
             rule_no    = 100
             action     = "allow"
             cidr_block = "0.0.0.0/0"
             from_port  = 0
             to_port    = 0
             protocol   = "-1"
          }
        ingress {
             rule_no    = 100
             action     = "allow"
             cidr_block = "0.0.0.0/0"
             from_port  = 0
             to_port    = 0
             protocol   = "-1"
          }