AWS VPC Security Hardening: Network Isolation & IAM Best Practices

AWS Virtual Private Cloud (VPC) represents the foundation of your network security boundary in the cloud. Unsecured or default configurations leave database ports exposed and allow unrestricted ingress paths. In this engineering guide, we walk through the steps required to secure your cloud perimeter.

1. Multi-Tier Subnet Architecture

An enterprise-ready VPC should segregate workloads into three distinct tiers:

Public Subnet Tier: Holds internet-facing resources (ALBs, NAT Gateways).
Private App Subnet Tier: Holds application services (Next.js backends, container runtimes).
Isolated Database Subnet Tier: Completely cut off from the internet, containing databases (MongoDB, PostgreSQL) and cash nodes.

                  ┌───────────────────────┐
                  │   Internet Gateway    │
                  └───────────┬───────────┘
                              │
            ┌─────────────────▼─────────────────┐
            │   Public Subnets (ALB, NAT GW)    │
            └─────────────────┬─────────────────┘
                              │ NAT Routed
            ┌─────────────────▼─────────────────┐
            │   Private App Subnets (Express)   │
            └─────────────────┬─────────────────┘
                              │ Internal Only
            ┌─────────────────▼─────────────────┐
            │  Isolated DB Subnets (MongoDB)   │
            └───────────────────────────────────┘

2. Stateless vs Stateful Rules

We configure:

NACLs on subnet borders to block known bad IPs or restrict CIDR blocks.
Security Groups to enforce tight microsegmentation between specific resource groups.

3. Terraform Code Snippet

Here is how we define the private VPC setup with Terraform:

module "vpc" {
  source  = "terraform-aws-modules/vpc/aws"
  version = "5.0.0"

  name = "ajitdev-prod-vpc"
  cidr = "10.0.0.0/16"

  azs             = ["us-east-1a", "us-east-1b"]
  private_subnets = ["10.0.1.0/24", "10.0.2.0/24"]
  public_subnets  = ["10.0.101.0/24", "10.0.102.0/24"]

  enable_nat_gateway = true
  single_nat_gateway = true
}

1. Multi-Tier Subnet Architecture

An enterprise-ready VPC should segregate workloads into three distinct tiers:

Public Subnet Tier: Holds internet-facing resources (ALBs, NAT Gateways).

Private App Subnet Tier: Holds application services (Next.js backends, container runtimes).

Isolated Database Subnet Tier: Completely cut off from the internet, containing databases (MongoDB, PostgreSQL) and cash nodes.

                  ┌───────────────────────┐
                  │   Internet Gateway    │
                  └───────────┬───────────┘
                              │
            ┌─────────────────▼─────────────────┐
            │   Public Subnets (ALB, NAT GW)    │
            └─────────────────┬─────────────────┘
                              │ NAT Routed
            ┌─────────────────▼─────────────────┐
            │   Private App Subnets (Express)   │
            └─────────────────┬─────────────────┘
                              │ Internal Only
            ┌─────────────────▼─────────────────┐
            │  Isolated DB Subnets (MongoDB)   │
            └───────────────────────────────────┘

3. Terraform Code Snippet

Here is how we define the private VPC setup with Terraform:

module "vpc" {
  source  = "terraform-aws-modules/vpc/aws"
  version = "5.0.0"

  name = "ajitdev-prod-vpc"
  cidr = "10.0.0.0/16"

  azs             = ["us-east-1a", "us-east-1b"]
  private_subnets = ["10.0.1.0/24", "10.0.2.0/24"]
  public_subnets  = ["10.0.101.0/24", "10.0.102.0/24"]

  enable_nat_gateway = true
  single_nat_gateway = true
}

AWS VPC Security Hardening: Network Isolation & IAM Best Practices

1. Multi-Tier Subnet Architecture

2. Stateless vs Stateful Rules

3. Terraform Code Snippet

Ajit Dev (@ajitdev01)

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AWS VPC Security Hardening: Network Isolation & IAM Best Practices

1. Multi-Tier Subnet Architecture

2. Stateless vs Stateful Rules

3. Terraform Code Snippet

Ajit Dev (@ajitdev01)

Related Engineering Articles

Building Production-Grade Microservices with Next.js 15, Docker & Kubernetes

Buddy CI/CD Complete Guide: Visual Pipelines, Docker Caching & Zero-Downtime Deployments

Buddy CI/CD vs GitHub Actions: Speed, Developer Experience & Pipeline Benchmarks