Security  

VPC, Subnets and Firewalls in Enterprise Cloud Network

Pre-requisite to understand this

  • IP addressing & CIDR – VPC and subnets are defined using CIDR blocks

  • Routing concepts – VPC controls traffic routing boundaries

  • Network isolation – VPC provides logical isolation per enterprise

  • Cloud shared responsibility – Provider manages infra, enterprise manages VPC

  • Security layers – VPC is the first isolation layer

Introduction

In an enterprise solution, the Virtual Private Cloud (VPC) is the core networking boundary that defines isolation, trust, and control. A VPC represents a dedicated virtual network for an enterprise, within which subnets, firewalls, routing tables, and gateways operate. Subnets divide the VPC into functional zones, while firewalls enforce security rules across and within these zones. Without a VPC, enterprises cannot guarantee isolation, compliance, or predictable network behavior. Hence, VPC is the foundation layer, and subnets and firewalls are control mechanisms built inside it.

What problem can we solve with this?

Enterprises struggle with shared infrastructure risks, uncontrolled access, regulatory compliance, and scaling secure systems. VPC solves the fundamental problem of network isolation, ensuring one enterprise’s workloads are logically separated from others. Within the VPC, subnets enable workload separation by tier, and firewalls restrict network traffic. This layered approach prevents lateral movement of threats, enforces governance, and enables enterprises to confidently deploy mission-critical applications at scale.

Problems solved:

  • Enterprise isolation – VPC separates one organization from others

  • Controlled network boundary – All traffic enters/exits via VPC

  • Environment separation – Prod, Dev, Test in different VPCs

  • Reduced attack surface – No default public exposure

  • Regulatory compliance – Dedicated address space & controls

  • Secure hybrid connectivity – VPC to on-prem integration

How to implement/use this?

Implementation always starts with VPC design. The enterprise defines a CIDR block that becomes the private address space. Subnets are created inside the VPC to represent application tiers or security zones. Firewalls are attached at the VPC and subnet level to regulate traffic. Routing tables define how traffic flows within the VPC and to external networks. Applications are deployed into subnets based on exposure level, ensuring that all communication stays within the VPC unless explicitly allowed.

Implementation steps:

  • Create VPC – Defines enterprise network boundary

  • Define CIDR range – Controls IP allocation

  • Create subnets – Logical segmentation inside VPC

  • Attach firewalls – Enforce security at VPC edge

  • Configure routing – Controls internal/external flow

  • Deploy workloads – Fully contained within VPC

Sequence Diagram

This sequence highlights the VPC as the mandatory traffic boundary. All traffic enters through the VPC gateway and is filtered by VPC-level firewall rules. Subnets do not exist independently; they operate strictly inside the VPC. Internal communication never leaves the VPC, ensuring low latency, security, and compliance. The database remains fully private within the VPC.

seq

Key points:

  • VPC is the entry and exit boundary

  • Firewalls protect the entire VPC

  • Subnets are internal VPC zones

  • No direct internet access to private resources

  • All east-west traffic stays inside VPC

  • Strong isolation and governance

Component Diagram

Here, the VPC is modelled as the top-level component, clearly showing that all enterprise services live inside it. Firewalls operate at the VPC edge, while subnets act as internal partitions. This makes it explicit that no component exists outside the VPC, reinforcing isolation and security ownership.

comp

Key points:

  • VPC is the parent container

  • Firewalls guard VPC perimeter

  • Subnets group components by trust level

  • Clear separation of concerns

  • Prevents accidental public exposure

  • Enterprise-grade network governance

Deployment Diagram

This deployment diagram shows the VPC as the enterprise deployment boundary inside the cloud provider. All infrastructure nodes are deployed within the VPC, ensuring that compute, databases, and services are never directly exposed. The firewall protects the VPC perimeter, while subnets define deployment zones for each tier.

depl

Key points

  • VPC is the enterprise deployment scope

  • All servers are deployed inside VPC

  • Firewall protects VPC perimeter

  • Subnets define deployment tiers

  • Strong isolation from other tenants

  • Enables secure scaling

Advantages

  1. Strong isolation – Dedicated enterprise network

  2. Security ownership – Full control of traffic rules

  3. Compliance ready – Meets audit requirements

  4. Scalable design – Easy subnet expansion

  5. Hybrid connectivity – VPN / Direct Connect support

  6. Reduced blast radius – Failures stay within VPC

Summary

In an enterprise solution, the VPC is the most critical building block, acting as the secure, isolated network foundation. Subnets structure workloads inside the VPC, and firewalls enforce strict access controls across its boundaries. Together, they create a layered, defense-in-depth architecture that supports scalability, compliance, and resilience. Without a VPC, subnets and firewalls lose context; with it, enterprises gain full control over their cloud networking strategy.

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