Creating VPC through terraform

Features

• Easy to customise and use.
• Each subnet CIDR block created through automation.
• Using tfvars file to access and modify variables.
• Project name is appended to the resources that are creating.

Prerequisites for this project

• Need AWS CLI access or IAM user access with attached policies for the creation of VPC.
• Terraform need to be installed in your system.
• Knowledge to the working principles of each AWS services especially VPC, EC2 and IP Subnetting.

Installation

If you need to download terraform , then click here Terraform .

Lets create a file for declaring the variables.This is used to declare the variable and the values are passing through the terrafrom.tfvars file.

Create a variables.tf file

variable "region" {}
variable "access_key" {}
variable "secret_key" {}
variable "vpc_cidr" {}
variable "project" {}

Create a provider.tf file

provider "aws" {
  region     = var.region
  access_key = var.access_key
  secret_key = var.secret_key
}

Create a terraform.tfvars

By default terraform.tfvars will load the variables to the the reources. You can modify accordingly as per your requirements.

region     = "put-your-region-here"
access_key = "put-your-access-key-here"
secret_key = "put-your-secret-key-here"
project = "name-of-your-project"
vpc_cidr = "X.X.X.X/X"

Go to the directory that you wish to save your tfstate files.Then Initialize the working directory containing Terraform configuration files using below command.

terraform init

Lets start creating main.tf file with the details below.

To create VPC

resource "aws_vpc" "vpc" {
  cidr_block           = var.vpc_cidr
  instance_tenancy     = "default"
  enable_dns_support   = true
  enable_dns_hostnames = true
  tags = {
    Name = "${var.project}-vpc"
  }
}

To Gather All Subnet Name

data "aws_availability_zones" "available" {
  state = "available"
}

To create InterGateWay For VPC

resource "aws_internet_gateway" "igw" {
  vpc_id = aws_vpc.vpc.id
  tags = {
    Name = "${var.project}-igw"
  }
}

Here in this infrastructre we shall create 3 public and 3 private subnets in the region.This sample was meant for regions having 6 availability zone. I have used "us-east-1". Choose your region and modify according to the availability of the AZ. Also we have already provided the CIDR block in our terraform.tfvars you dont need to calculate the subnets, here we use terraform to automate the subnetting in /19.

Creating public1 Subnet

resource "aws_subnet" "public1" {
    
  vpc_id                   = aws_vpc.vpc.id
  cidr_block               = cidrsubnet(var.vpc_cidr, 3, 0)
  availability_zone        = element(data.aws_availability_zones.available.names,0)
  map_public_ip_on_launch  = true
  tags = {
    Name = "${var.project}-public1"
  }
}

Creating public2 Subnet

resource "aws_subnet" "public2" {
  vpc_id                   = aws_vpc.vpc.id
  cidr_block               = cidrsubnet(var.vpc_cidr, 3, 1)
  availability_zone        = element(data.aws_availability_zones.available.names,1)
  map_public_ip_on_launch  = true
  tags = {
    Name = "${var.project}-public2"
  }
}

Creating public3 Subnet

resource "aws_subnet" "public3" {
  vpc_id                   = aws_vpc.vpc.id
  cidr_block               = cidrsubnet(var.vpc_cidr, 3, 2)
  availability_zone        = element(data.aws_availability_zones.available.names,2)
  map_public_ip_on_launch  = true
  tags = {
    Name = "${var.project}-public-3"
  }
}

Creating private1 Subnet

resource "aws_subnet" "private1" {
  vpc_id                   = aws_vpc.vpc.id
  cidr_block               = cidrsubnet(var.vpc_cidr, 3, 3)
  availability_zone        = element(data.aws_availability_zones.available.names,3)
  map_public_ip_on_launch  = false
  tags = {
    Name = "${var.project}-private1"
  }
}

Creating private2 Subnet

resource "aws_subnet" "private2" {
  vpc_id                   = aws_vpc.vpc.id
  cidr_block               = cidrsubnet(var.vpc_cidr, 3, 4)
  availability_zone        = element(data.aws_availability_zones.available.names,4)
  map_public_ip_on_launch  = false
  tags = {
    Name = "${var.project}-private2"
  }
}

Creating private3 Subnet

resource "aws_subnet" "private3" {
  vpc_id                   = aws_vpc.vpc.id
  cidr_block               = cidrsubnet(var.vpc_cidr, 3, 5)
  availability_zone        = element(data.aws_availability_zones.available.names,5)
  map_public_ip_on_launch  = false
  tags = {
    Name = "${var.project}-private3"
  }
}

Creating Elastic IP For Nat Gateway

resource "aws_eip" "eip" {
  vpc      = true
  tags     = {
    Name = "${var.project}-eip"
  }
}

Attaching Elastic IP to NAT gateway

resource "aws_nat_gateway" "nat" {
  allocation_id = aws_eip.eip.id
  subnet_id     = aws_subnet.public1.id
  tags = {
    Name = "${var.project}-nat"
  }
}

Creating Public Route Table

resource "aws_route_table" "public" {
  vpc_id = aws_vpc.vpc.id
  route {
    cidr_block = "0.0.0.0/0"
    gateway_id = aws_internet_gateway.igw.id
  }
  tags = {
    Name = "${var.project}-public"
  }
}

Creating Private Route Table

  resource "aws_route_table" "private" {
  vpc_id = aws_vpc.vpc.id
  route {
    cidr_block = "0.0.0.0/0"
    nat_gateway_id = aws_nat_gateway.nat.id
  }
  tags = {
    Name = "${var.project}-private"
  }
}

Creating Public Route Table Association

resource "aws_route_table_association" "public1" {        
  subnet_id      = aws_subnet.public1.id
  route_table_id = aws_route_table.public.id
}
resource "aws_route_table_association" "public2" {      
  subnet_id      = aws_subnet.public2.id
  route_table_id = aws_route_table.public.id
}
resource "aws_route_table_association" "public3" {       
  subnet_id      = aws_subnet.public3.id
  route_table_id = aws_route_table.public.id
}

Creating Private Route Table Association

resource "aws_route_table_association" "private1" {        
  subnet_id      = aws_subnet.private1.id
  route_table_id = aws_route_table.private.id
}
resource "aws_route_table_association" "private2" {      
  subnet_id      = aws_subnet.private2.id
  route_table_id = aws_route_table.private.id
}
resource "aws_route_table_association" "private3" {       
  subnet_id      = aws_subnet.private3.id
  route_table_id = aws_route_table.private.id
}

Create an output.tf for getting terrafrom output.

output "aws_eip" {
value = aws_eip.eip.public_ip
}
output "aws_vpc" {
value = aws_vpc.vpc.id
}
output "aws_internet_gateway" {
value = aws_internet_gateway.igw.id
}
output "aws_nat_gateway" {
value = aws_nat_gateway.nat.id
}
output "aws_route_table_public" {
value = aws_route_table.public.id
}
output "aws_route_table_private" {
value = aws_route_table.private.id
}

Lets validate the terraform files using

terraform validate

Lets plan the architecture and verify once again.

terraform plan

Lets apply the above architecture to the AWS.

terraform apply