Build a Custom VPC with Public & Private Subnets in AWS Using Terraform

If you’re diving into AWS networking or practicing Infrastructure as Code (IaC), setting up a custom VPC from scratch with Terraform is a great hands-on project. In this guide, we’ll walk through how to:

• Create a VPC

• Add public and private subnets

• Attach an internet gateway

• Configure a routing table

• Launch an EC2 instance in the public subnet

Let’s get started! 🔧

Terraform Project Setup

1️⃣ Terraform Configuration

Start with your main.tf file, which defines the required provider and sets the AWS region:

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "6.0.0-beta2"
    }
  }
}

provider "aws" {
  region = "us-east-2"
}

Create VPC and Subnets

2️⃣ Create a VPC

We’ll create a VPC with a /16 CIDR block:

resource "aws_vpc" "my-vpc" {
  cidr_block = "10.0.0.0/16"

  tags = {
    Name = "my_vpc"
  }
}

3️⃣ Define Subnets

• Private Subnet:

resource "aws_subnet" "private-subnet" {
  cidr_block = "10.0.1.0/24"
  vpc_id     = aws_vpc.my-vpc.id

  tags = {
    Name = "private-subnet"
  }
}

• Public Subnet:

resource "aws_subnet" "public-subnet" {
  cidr_block = "10.0.2.0/24"
  vpc_id     = aws_vpc.my-vpc.id

  tags = {
    Name = "public-subnet"
  }
}

Internet Access

4️⃣ Add Internet Gateway

We’ll need an internet gateway so instances in the public subnet can access the internet:

resource "aws_internet_gateway" "my-igw" {
  vpc_id = aws_vpc.my-vpc.id

  tags = {
    Name = "my-igw"
  }
}

5️⃣ Create Route Table & Associate

This route table allows public subnet traffic to route through the internet gateway:

resource "aws_route_table" "my-rt" {
  vpc_id = aws_vpc.my-vpc.id

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

resource "aws_route_table_association" "public-sub" {
  route_table_id = aws_route_table.my-rt.id
  subnet_id      = aws_subnet.public-subnet.id
}

💻 Launch EC2 Instance in Public Subnet

To verify the setup works, we’ll launch a simple EC2 instance in the public subnet.

resource "aws_instance" "server28" {
  ami           = "ami-06c8f2ec674c67112" # Amazon Linux 2 AMI (example)
  instance_type = "t2.micro"
  subnet_id     = aws_subnet.public-subnet.id

  tags = {
    Name = "tfserver1"
  }
}

Note: Ensure the AMI ID is valid for your selected region (us-east-2 in this case). You can find the latest AMI IDs from the AWS Console or AMI Marketplace.

---

Terraform Commands in Action

Now that your infrastructure is defined, it’s time to run the Terraform workflow:

Project Directory Setup

Make sure you are in the correct working directory:

cd Terraform_vpc/aws-vpc

(Optional: If you’re using environment variables, source them first.)

source .env

1️⃣ Initialize Terraform

terraform init

This downloads the required provider plugins and sets up the backend.

2️⃣ Validate Your Code

terraform validate

Confirms that your configuration is syntactically correct.

3️⃣ Apply the Plan

terraform apply

You’ll see a detailed plan, and when prompted, type:

yes

Once completed, you’ll get confirmation that resources were created:

Apply complete! Resources: 6 added, 0 changed, 0 destroyed.

Later, to add the EC2 instance:

terraform apply

Output:

Apply complete! Resources: 1 added, 0 changed, 0 destroyed.

Success! You now have a fully functional VPC with an EC2 instance in the public subnet.

Main points

• A custom VPC with CIDR 10.0.0.0/16

• One private and one public subnet

• An Internet Gateway connected to the public subnet

• A Route Table for internet access

• A t2.micro EC2 instance deployed in the public subnet

Cleanup (Optional)

When you're done testing, clean up the resources to avoid unnecessary costs:

terraform destroy

Thanks for Reading!

Hope this gives you some perspective.

Coming Up Next:

More hands-on cloud projects and DevOps tips — stay tuned!

Let’s Connect:

Share your thoughts in the comments or reach out on LinkedIn. Your feedback means a lot! You can also check out my work on GitHub.