• Manually setup VPC

Via terraform

Resource mapping shows how it works and what created after doing all stuff

What We're Building

VPC (10.0.0.0/16)
├── Private Subnet (10.0.0.0/24)  → No internet access
├── Public Subnet  (10.0.2.0/24)  → Has internet access
├── Internet Gateway               → Connects VPC to internet
└── Route Table → Public Subnet → IGW → Internet 

CIDR Block -

10.0.0.0/16  → VPC range (large - 65,536 IPs)
10.0.1.0/24  → Subnet range (small - 256 IPs)
0.0.0.0/0    → All internet traffic (any IP)

Rule: Subnets must be within VPC CIDR range

Complete Code (main.tf)

provider "aws" {
  region = "eu-north-1"
}

# -----------------------------------------------
# STEP 1: Create VPC
# Like creating your own private network in AWS
# Manual: VPC → Create VPC → add CIDR
# -----------------------------------------------
resource "aws_vpc" "my-vpc" {
  cidr_block = "10.0.0.0/16"   # IP range for entire network

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

# -----------------------------------------------
# STEP 2: Create Private Subnet
# Internal only - no internet (for DB, backend)
# Manual: Subnet → Create → pick VPC → add CIDR
# -----------------------------------------------
resource "aws_subnet" "private-subnet" {
  cidr_block = "10.0.0.0/24"        # IP range within VPC
  vpc_id     = aws_vpc.my-vpc.id    # Which VPC it belongs to

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

# -----------------------------------------------
# STEP 3: Create Public Subnet
# Internet accessible (for web servers, LBs)
# -----------------------------------------------
resource "aws_subnet" "public-subnet" {
  cidr_block = "10.0.2.0/24"        # Different range from private
  vpc_id     = aws_vpc.my-vpc.id

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

# -----------------------------------------------
# STEP 4: Create Internet Gateway
# Door between your VPC and the internet
# Manual: IGW → Create → Actions → Attach to VPC
# -----------------------------------------------
resource "aws_internet_gateway" "my-igw" {
  vpc_id = aws_vpc.my-vpc.id   # Attach to VPC directly in Terraform

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

# -----------------------------------------------
# STEP 5: Create Route Table
# Rules for traffic - where should it go?
# cidr 0.0.0.0/0 = all internet traffic → send to IGW
# Manual: Route Table → Create → Edit Routes → add IGW
# -----------------------------------------------
resource "aws_route_table" "my-rt" {
  vpc_id = aws_vpc.my-vpc.id

  route {
    cidr_block = "0.0.0.0/0"                    # All internet traffic
    gateway_id = aws_internet_gateway.my-igw.id  # Send it to IGW
  }
}

# -----------------------------------------------
# STEP 6: Associate Public Subnet with Route Table
# Links public subnet to route table → gives it internet
# Private subnet not associated = no internet 
# Manual: Route Table → Subnet Associations → Edit
# -----------------------------------------------
resource "aws_route_table_association" "public-sub" {
  route_table_id = aws_route_table.my-rt.id       # Which route table
  subnet_id      = aws_subnet.public-subnet.id    # Which subnet
}

# -----------------------------------------------
# STEP 7: Launch EC2 Instance in Public Subnet
# subnet_id puts it inside our public subnet
# Without subnet_id → goes to default VPC
# -----------------------------------------------
resource "aws_instance" "myserver2" {
  ami           = "ami-0c83cb1c664994bbd"
  instance_type = "t3.nano"
  subnet_id     = aws_subnet.public-subnet.id  # Place inside public subnet

  tags = {
    Name = "SampleServer"
  }
}

Key Concepts

Why two subnets?

Public Subnet  → Route Table has IGW → Internet 
Private Subnet → No route table attached → No Internet 

• Public → Web servers, load balancers (need internet)
• Private → Databases, backend servers (should NOT be public)

Why 0.0.0.0/0 in route?