Day 03 – Building a VPC with Public & Private Subnets in Terraform

Yesterday, I built my first custom VPC with a single subnet. Today, I went deeper into AWS networking by creating a VPC with both a public and private subnet, plus an Internet Gateway and a Route Table.

By the end of the day, I had a network ready to host internet-facing resources (in the public subnet) and secure resources (in the private subnet).

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🔹 What is a VPC?

A VPC (Virtual Private Cloud) is your private, isolated network inside AWS. You can create subnets, attach gateways, and control access to your infrastructure.

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🔹 Terraform Code

Here’s the code I used for today’s setup:

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "6.9.0"
    }
  }
}

provider "aws" {
  region = "ap-south-1"
}

# VPC
resource "aws_vpc" "my_vpc" {
  cidr_block = "10.0.0.0/16"
  tags = {
    Name = "my_vpc"
  }
}

# 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
  map_public_ip_on_launch = true
  tags = {
    Name = "public-subnet"
  }
}

# Internet Gateway
resource "aws_internet_gateway" "my-igw" {
  vpc_id = aws_vpc.my_vpc.id
  tags = {
    Name = "my-igw"
  }
}

# Route Table
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
  }
}

# Route Table Association (Public Subnet)
resource "aws_route_table_association" "public-sub" {
  route_table_id = aws_route_table.my-rt.id
  subnet_id      = aws_subnet.public-subnet.id
}

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🔹 What’s Happening Here?

• VPC → Main network (10.0.0.0/16)

• Private Subnet → Internal-only resources (10.0.1.0/24)

• Public Subnet → Internet-facing resources (10.0.2.0/24)

• Internet Gateway → Allows internet access

• Route Table → Sends outbound traffic from public subnet to internet

• Route Table Association → Connects the public subnet with the route table

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▶️ Terraform Commands I Used

terraform init       # Initialize project
terraform validate   # Validate code
terraform plan       # Preview resources
terraform apply      # Deploy VPC + Subnets + IGW + Route Table
terraform destroy    # Tear it all down

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💡 Key Takeaways

• A VPC is the foundation of AWS networking.

• Public subnets are for internet-facing resources like web servers.

• Private subnets are for secure resources like databases.

• Internet Gateway + Route Table is what gives your public subnet internet access.

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🔗 Follow My Journey
📖 Blog Series: Terraform with AWS
💻 Code: GitHub
🐦 Updates: X (Twitter)

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