Creating VPCs and Subnets with Terraform and IaC

Introduction

In this exercise, we will walk through the process of creating a basic infrastructure on AWS using Terraform, an open-source Infrastructure as Code (IaC) tool. Specifically, we'll create a Virtual Private Cloud (VPC) with two subnets, a public and a private one. We will also create an Internet gateway and a route table, which will be associated with our public subnet. This setup mimics a typical cloud infrastructure configuration, separating resources into public and private subnets for improved security and control.

Desired Outcome

If you wish to give it a shot before looking into the detailed step-by-step and the solution videos, here is an overview of what the created solution should deploy:

A VPC with a CIDR block of 10.0.0.0/16.
One public subnet with a CIDR block of 10.0.0.0/24.
One private subnet with a CIDR block of 10.0.1.0/24.
One Internet Gateway.
One public route table with a route to the Internet Gateway, and the correct association between the public subnet and the public route table.

Useful Resources

AWS Terraform Provider: https://registry.terraform.io/providers/hashicorp/aws

Step-by-Step Guide

Begin by initializing your Terraform configuration with the terraform block. This block sets up the necessary details regarding the providers that will be used in your configuration. In this case, the AWS provider is required.
```
terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
    }
  }
}
```
Next, set up your AWS provider with the provider block. Here, you need to specify the region in which your resources will be created.
```
provider "aws" {
  region = "eu-west-1"
}
```
Create a VPC using the aws_vpc resource. You need to specify a CIDR block for your VPC, as well as the Name tag with the value Terraform VPC.
```
resource "aws_vpc" "demo_vpc" {
  cidr_block = "10.0.0.0/16"

  tags = {
    Name = "Terraform VPC"
  }
}
```

Then, create two subnets within this VPC using the aws_subnet resource. Make sure to reference your VPC ID and set an appropriate CIDR block for each subnet.

resource "aws_subnet" "public_subnet" {
  vpc_id     = aws_vpc.demo_vpc.id
  cidr_block = "10.0.0.0/24"
}

resource "aws_subnet" "private_subnet" {
  vpc_id     = aws_vpc.demo_vpc.id
  cidr_block = "10.0.1.0/24"
}

Next, create an Internet gateway and attach it to your VPC with the aws_internet_gateway resource.
```
resource "aws_internet_gateway" "igw" {
  vpc_id = aws_vpc.demo_vpc.id
}
```

Create a route table for your public subnet using the aws_route_table resource. This table will direct all traffic (0.0.0.0/0) to the Internet gateway.

resource "aws_route_table" "public_rtb" {
  vpc_id = aws_vpc.demo_vpc.id

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

Finally, associate the route table with your public subnet using the aws_route_table_association resource.

resource "aws_route_table_association" "public_subnet" {
  subnet_id      = aws_subnet.public_subnet.id
  route_table_id = aws_route_table.public_rtb.id
}

Congratulations on Completing the Exercise!

Well done on successfully creating a basic infrastructure on AWS using Terraform. You've shown great understanding of Infrastructure as Code (IaC) and how to use Terraform to create and manage a VPC with subnets and Internet gateway on AWS. Keep up the good work and continue to expand your knowledge in this area. You're doing fantastic!