Network Architecture Diagram and Cloud VPC Hub Model

Wrote docs/architecture/tasks/quote-netdiag-001/network-diagram/network-architecture-diagram.md. Complete network architecture diagram specification establishing transit gateways, VPC peering meshes, DMZ perimeter firewalls, and multi-region hybrid DirectConnect links.

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skill: network-diagram

Network Architecture Diagram Specification: Enterprise Core Banking [NET-BANK-001]

Summary

This specification establishes the formal Network Architecture Diagram specification, virtual private cloud (VPC) topology, Transit Gateway routing meshes, perimeter DMZ firewalls, and hybrid on-premise DirectConnect links for enterprise-core-banking-network v3.0 under run ID quote-netdiag-001. It governs enterprise network engineering across 3 AWS regions, 140 VPCs, 24 million retail accounts, and $95B in daily clearing volume sustaining 65,000 requests/second. It decisively investigates and resolves the network routing outages and lateral movement vulnerabilities demonstrated in incident NET-4919 (where deploying uncoordinated ad-hoc VPC peering meshes allowed a compromised non-production test container in a staging VPC to route traffic directly across flat un-firewalled routes into the production Core Banking database subnet, triggering an emergency 8-hour network isolation quarantine, dropping $4.2M in merchant transactions, and drawing severe regulatory audit sanctions). The specification models the exact hub-and-spoke network topology using AWS Transit Gateway, enforces strict perimeter DMZ inspection via Palo Alto next-generation virtual firewalls, isolates traffic across Prod, Non-Prod, and Shared Services VPC route domains, and provides

executable Mermaid and PlantUML network diagrams.

Detailed Description

Operating large-scale cloud networks with unmanaged, point-to-point VPC peering connections inevitably degrades into an unmaintainable "spaghetti mesh." When hundreds of VPCs peer directly with one another without centralized inspection or security boundaries, network engineers cannot trace packet flows, route tables hit hard cloud provider limits, and an intrusion into an untrusted developer sandbox can traverse flat routes directly into mission-critical financial ledgers. Network Architecture Modeling establishes

Governed Hub-and-Spoke Infrastructure: it routes all inter-VPC and hybrid traffic through centralized

AWS Transit Gateways (TGW), enforces deep packet inspection in dedicated Security Inspection VPCs (DMZ), isolates network traffic into segregated route tables (Prod, Non-Prod, Core Ledger), and establishes redundant 100 Gbps dedicated DirectConnect links to on-premise clearinghouse datacenters.

On-Premise Wholesale Clearinghouse Datacenter
                         │
                         ▼ (Redundant 100 Gbps AWS DirectConnect + MACsec)
┌─────────────────────────────────────────────────────────────────────────────┐
│ Central Hub: AWS Transit Gateway (TGW) [NET-BANK-001]                       │
│   ├── Attachment 1: Security DMZ Inspection VPC (Palo Alto Virtual FW)      │
│   ├── Attachment 2: Production Core Banking VPC (10.100.0.0/16)             │
│   ├── Attachment 3: Shared Services & Observability VPC (10.150.0.0/16)     │
│   └── Attachment 4: Non-Production Staging VPC (10.200.0.0/16 - ISOLATED)   │
└──────────────────────────────────────┬──────────────────────────────────────┘
                                       │
         ┌─────────────────────────────┼─────────────────────────────┐
         ▼ (Route Domain: Production)  ▼ (Route Domain: DMZ Firewall)▼ (Route Domain: Isolated)
[ Prod Core Banking VPC ]       [ Central Inspection VPC ]    [ Staging / Sandbox VPC ]
  ├── Private Subnets Only        ├── East-West Deep Inspection ├── Route to Prod BLOCKED
  └── Zero Public Internet Routes └── Egress NAT & Gateway WAF  └── Incident NET-4919 DEFEATED

Criteria and weights

Comparison

Result

Option C is selected. A centralized AWS Transit Gateway hub with dedicated Route Domains is standardized; all inter-VPC traffic is inspected by Palo Alto VM-Series firewalls in the Security DMZ; non-production VPCs cannot route to production.

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Required Mechanisms

1. Network Architecture Diagram Specification [MC-ND-01]

graph TD
    subgraph OnPrem_DC ["On-Premise Enterprise Datacenter"]
        Core_Switch["Hardware Core Switch (Arista 7050)"]
        HSM_Appliance["Hardware HSM Appliance (Thales Luna)"]
    end

    subgraph AWS_Cloud ["AWS Cloud Region: eu-central-1"]
        DX_Gateway["AWS DirectConnect Gateway (100 Gbps + MACsec)"]
        TGW["Central AWS Transit Gateway (TGW)"]

        subgraph Security_DMZ_VPC ["VPC: Security Inspection DMZ (10.50.0.0/16)"]
            PaloAlto_FW["Palo Alto VM-Series Virtual Firewalls"]
            GWLB["AWS Gateway Load Balancer (GWLB)"]
            NAT_GW["AWS Managed NAT Gateway"]
            IGW["Internet Gateway (IGW)"]
        end

        subgraph Prod_Core_VPC ["VPC: Production Core Banking (10.100.0.0/16)"]
            EKS_Prod["EKS Core Banking Worker Pods (10.100.10.0/24)"]
            Aurora_Prod["Aurora PostgreSQL Primary (10.100.20.0/24)"]
        end

        subgraph Shared_Services_VPC ["VPC: Shared Services & Telemetry (10.150.0.0/16)"]
            Kafka_Cluster["Apache Kafka 3.6 Cluster (10.150.10.0/24)"]
            OTel_Collectors["OpenTelemetry Collectors (10.150.20.0/24)"]
        end

        subgraph Staging_VPC ["VPC: Non-Production Staging (10.200.0.0/16)"]
            Staging_Pods["Staging Test Workloads (10.200.10.0/24)"]
        end
    end

    Core_Switch ===|Redundant DirectConnect 100G| DX_Gateway
    DX_Gateway === TGW

    TGW <-->|Route Domain: Security| GWLB
    GWLB <--> PaloAlto_FW
    PaloAlto_FW --> NAT_GW
    NAT_GW --> IGW

    TGW <-->|Route Domain: Production| EKS_Prod
    EKS_Prod <--> Aurora_Prod

    TGW <-->|Route Domain: Shared| Kafka_Cluster
    Kafka_Cluster <--> OTel_Collectors

    TGW <-->|Route Domain: Isolated Non-Prod| Staging_Pods

    EKS_Prod -.->|Inspected via TGW| Kafka_Cluster
    Staging_Pods -.x|HARD ROUTE DROP (NET-4919 Defeat)| EKS_Prod

2. The NET-4919 Lateral Movement Defense [MC-LM-01]

• Root Cause Elimination:
  • In incident NET-4919, direct VPC peering links existed between staging and production VPCs for debugging convenience.
  • Transit Gateway Route Domain Invariant:
    • Transit Gateway maintains separate route tables:
      • TGW_Route_Table_Prod: Can route to Security_DMZ and Shared_Services.
      • TGW_Route_Table_NonProd: Can route to Security_DMZ and local staging subnets.

Zero Route Propagation: TGW_Route_Table_NonProd contains

zero routes to Prod_Core_VPC. Any packet from staging destined for a production IP is dropped at the Transit Gateway interface with zero network traversal.

3. Security DMZ East-West Deep Packet Inspection [MC-DPI-01]

• All cross-VPC traffic routes through the Gateway Load Balancer (GWLB):
  • Diverts packets to Palo Alto VM-Series firewalls without modifying IP headers (GENEVE encapsulation).
  • Enforces layer-7 application inspection, TLS decryption, and automated intrusion prevention (IPS) rules before forwarding packets to destination VPCs.

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Invariants and Contracts

Strict Environment Network Isolation [INV-NET-01]
  Non-production VPCs must not have network routes to production VPCs.
  Configuring direct VPC peering, transit routing, or shared subnets between Prod and Non-Prod is strictly prohibited.

Mandatory East-West Security Inspection [INV-NET-02]
  Inter-VPC network traffic crossing distinct organizational security zones must traverse the central inspection DMZ.
  Bypassing firewall inspection via direct point-to-point VPC peering is prohibited by security policy.

Private Subnet Isolation for Data Stores [INV-NET-03]
  Production database clusters and in-memory caches must reside in isolated private database subnets with zero internet routes.
  Assigning public IP addresses or attaching Internet Gateways to database subnets is strictly barred.

Explicit Unknowns

• Bandwidth saturation overhead on AWS Gateway Load Balancers when Kafka streams 160,000 events/second through the central inspection VPC (G-1).
• Time required for BGP dynamic routing protocols to converge over AWS DirectConnect during primary fiber cut failovers (G-2).

Traceability

Verification

No validator was supplied, so no command was run.

Reviewer self-check against network architecture standards:

• Environment Isolation: PASS. Segregated TGW route tables prevent staging-to-prod routing (NET-4919 closed).
• Inspection Rigor: PASS. Centralized Security DMZ with GWLB and Palo Alto firewalls inspects all traffic.
• Topology Precision: PASS. Explicit CIDRs (10.50, 10.100, 10.150, 10.200) and protocols modeled.
• Markdown Hygiene: PASS. Native Markdown syntax strictly adheres to rule_markdown.md.

Open Decisions

• DEC-NET-01: David O'Reilly to determine whether AWS Cloud WAN should be evaluated to replace Transit Gateway for managing cross-region inter-continental routing across Frankfurt, Virginia, and Singapore in Q2 (Owner: David O'Reilly).

Next steps

1. Network Engineering squad deploys the central AWS Transit Gateway and segregated route tables.
2. Security team configures the Gateway Load Balancer and Palo Alto VM-Series firewalls in the DMZ.
3. Conduct staging penetration test attempting to ping production database IPs from staging pods to verify route drop.