SYSTEM_ARCHITECTURE.md

AegisPay System Architecture

Table of Contents

• System Overview
• High-Level Architecture
• Component Architecture
• Payment Flow Architecture
• State Machine Architecture
• Event-Driven Architecture
• Resilience Architecture
• Data Flow Architecture
• Distributed Systems Architecture
• Deployment Architecture

---

System Overview

AegisPay is an enterprise-grade payment orchestration platform built on principles of distributed systems, event sourcing, and functional programming. It provides mission-critical reliability for high-volume payment processing.

graph TB
    subgraph "Client Applications"
        A[E-Commerce Platform]
        B[Mobile App]
        C[POS System]
        D[Subscription Service]
    end

    subgraph "AegisPay SDK"
        E[Payment API]
        F[Orchestration Engine]
        G[Gateway Registry]
        H[State Machine]
    end

    subgraph "Payment Gateways"
        I[Gateway A]
        J[Gateway B]
        K[Gateway C]
    end

    subgraph "Infrastructure"
        L[(Event Store)]
        M[(Database)]
        N[Message Queue]
        O[Metrics & Logs]
    end

    A --> E
    B --> E
    C --> E
    D --> E

    E --> F
    F --> G
    F --> H

    G --> I
    G --> J
    G --> K

    F --> L
    F --> M
    F --> N
    F --> O

    style E fill:#4CAF50
    style F fill:#2196F3
    style H fill:#FF9800
    style L fill:#9C27B0

Loading

---

High-Level Architecture

Multi-Layer Architecture with Clear Separation of Concerns

flowchart TB
    subgraph "API Layer"
        A1[PaymentService API]
        A2[TransactionalPaymentService]
        A3[IdempotentPaymentService]
    end

    subgraph "Application Layer"
        B1[Orchestration Engine]
        B2[Intelligent Router]
        B3[Retry Policy Manager]
        B4[Circuit Breaker]
        B5[Chaos Engineering]
    end

    subgraph "Domain Layer"
        C1[Payment Aggregate]
        C2[State Machine]
        C3[Domain Events]
        C4[Business Rules]
    end

    subgraph "Infrastructure Layer"
        D1[Event Store]
        D2[Distributed Lock Manager]
        D3[Transactional Outbox]
        D4[Observability System]
        D5[Idempotency Store]
    end

    subgraph "Gateway Layer"
        E1[Gateway Registry]
        E2[Gateway Adapters]
        E3[Health Monitor]
    end

    subgraph "External Systems"
        F1[Payment Gateway 1]
        F2[Payment Gateway 2]
        F3[Payment Gateway 3]
        F4[Event Bus/Kafka]
        F5[Monitoring Systems]
    end

    A1 --> B1
    A2 --> B1
    A3 --> B1

    B1 --> B2
    B1 --> B3
    B1 --> B4
    B1 --> B5

    B1 --> C1
    C1 --> C2
    C1 --> C3
    C2 --> C4

    B1 --> D1
    B1 --> D2
    B1 --> D3
    B1 --> D4
    B1 --> D5

    B2 --> E1
    E1 --> E2
    E2 --> E3

    E2 --> F1
    E2 --> F2
    E2 --> F3

    D3 --> F4
    D4 --> F5

    style C1 fill:#FF6B6B
    style C2 fill:#FF6B6B
    style B1 fill:#4ECDC4
    style D1 fill:#95E1D3
    style D3 fill:#95E1D3

Loading

---

Component Architecture

Core Component Interaction and Responsibilities

graph LR
    subgraph "Client Layer"
        Client[Client Application]
    end

    subgraph "API & Validation"
        API[Payment Service API]
        Validator[Input Validator]
        IdempotencyCheck[Idempotency Guard]
    end

    subgraph "Orchestration Core"
        Orchestrator[Payment Orchestrator]
        Router[Intelligent Router]
        FraudCheck[Fraud Detection]
        Hooks[Extensibility Hooks]
    end

    subgraph "Execution & Resilience"
        Retry[Retry Engine]
        CB[Circuit Breaker]
        Timeout[Timeout Manager]
        Fallback[Fallback Handler]
    end

    subgraph "State Management"
        StateMachine[State Machine]
        OptLock[Optimistic Lock]
        DistLock[Distributed Lock]
    end

    subgraph "Persistence & Events"
        EventStore[Event Store]
        Outbox[Transactional Outbox]
        DB[(Payment DB)]
    end

    subgraph "Gateway Management"
        GatewayRegistry[Gateway Registry]
        HealthMonitor[Health Monitor]
        GatewayAdapter[Gateway Adapter]
    end

    subgraph "Observability"
        Logger[Structured Logger]
        Metrics[Metrics Collector]
        Tracer[Distributed Tracer]
    end

    Client --> API
    API --> Validator
    Validator --> IdempotencyCheck
    IdempotencyCheck --> Orchestrator

    Orchestrator --> Router
    Orchestrator --> FraudCheck
    Orchestrator --> Hooks

    Router --> Retry
    Retry --> CB
    CB --> Timeout
    Timeout --> Fallback

    Orchestrator --> StateMachine
    StateMachine --> OptLock
    StateMachine --> DistLock

    StateMachine --> EventStore
    EventStore --> Outbox
    StateMachine --> DB

    Router --> GatewayRegistry
    GatewayRegistry --> HealthMonitor
    GatewayRegistry --> GatewayAdapter

    Orchestrator --> Logger
    Orchestrator --> Metrics
    Orchestrator --> Tracer

    style Orchestrator fill:#FFD93D
    style StateMachine fill:#FF6B6B
    style EventStore fill:#6BCB77
    style CB fill:#4D96FF

Loading

---

Payment Flow Architecture

End-to-End Payment Processing Flow

sequenceDiagram
    participant Client
    participant API
    participant Validator
    participant IdempotencyGuard
    participant Orchestrator
    participant Router
    participant StateMachine
    participant DistributedLock
    participant CircuitBreaker
    participant Gateway
    participant EventStore
    participant Outbox
    participant MessageBus

    Client->>API: processPayment(request)

    rect rgb(240, 248, 255)
        Note over API,Validator: Validation Phase
        API->>Validator: validate(request)
        Validator-->>API: ValidationResult
    end

    rect rgb(255, 248, 240)
        Note over API,IdempotencyGuard: Idempotency Check
        API->>IdempotencyGuard: check(idempotencyKey)
        alt Already Processed
            IdempotencyGuard-->>API: Return cached result
            API-->>Client: Payment result (cached)
        end
    end

    rect rgb(240, 255, 240)
        Note over Orchestrator,DistributedLock: Concurrency Control
        Orchestrator->>DistributedLock: acquireLock(paymentId)
        DistributedLock-->>Orchestrator: Lock acquired
    end

    rect rgb(255, 240, 245)
        Note over Orchestrator,Router: Routing Decision
        Orchestrator->>Router: selectGateway(payment, metrics)
        Router-->>Orchestrator: Gateway selection
    end

    rect rgb(248, 240, 255)
        Note over Orchestrator,StateMachine: State Transition
        Orchestrator->>StateMachine: transition(INITIATED → PROCESSING)
        StateMachine->>EventStore: append(PaymentInitiated)
        EventStore-->>StateMachine: Event persisted
        StateMachine-->>Orchestrator: State updated
    end

    rect rgb(255, 255, 240)
        Note over CircuitBreaker,Gateway: Gateway Execution
        Orchestrator->>CircuitBreaker: execute()
        CircuitBreaker->>Gateway: process(payment)

        alt Success
            Gateway-->>CircuitBreaker: Success response
            CircuitBreaker-->>Orchestrator: Success
        else Failure
            Gateway-->>CircuitBreaker: Error
            CircuitBreaker->>CircuitBreaker: Record failure
            CircuitBreaker-->>Orchestrator: Retry or fail
        end
    end

    rect rgb(240, 255, 255)
        Note over StateMachine,Outbox: Event Sourcing
        Orchestrator->>StateMachine: transition(PROCESSING → COMPLETED)
        StateMachine->>EventStore: append(PaymentCompleted)
        StateMachine->>Outbox: enqueue(PaymentCompleted)
        Outbox->>MessageBus: publish(event)
    end

    rect rgb(255, 240, 240)
        Note over Orchestrator,DistributedLock: Cleanup
        Orchestrator->>DistributedLock: releaseLock(paymentId)
        DistributedLock-->>Orchestrator: Lock released
    end

    Orchestrator-->>API: Payment result
    API-->>Client: Payment response

Loading

---

State Machine Architecture

Deterministic Finite Automaton for Payment States

stateDiagram-v2
    [*] --> INITIATED: Create Payment

    INITIATED --> PROCESSING: Start Processing
    INITIATED --> CANCELLED: Cancel Request
    INITIATED --> FAILED: Validation Failed

    PROCESSING --> AUTHORIZED: Gateway Auth Success
    PROCESSING --> FAILED: Gateway Auth Failed
    PROCESSING --> PROCESSING: Retry Attempt

    AUTHORIZED --> CAPTURED: Capture Funds
    AUTHORIZED --> CANCELLED: Cancel Auth
    AUTHORIZED --> EXPIRED: Auth Timeout

    CAPTURED --> COMPLETED: Settlement Success
    CAPTURED --> FAILED: Settlement Failed

    COMPLETED --> REFUND_INITIATED: Refund Request
    COMPLETED --> PARTIALLY_REFUNDED: Partial Refund

    REFUND_INITIATED --> REFUNDED: Refund Success
    REFUND_INITIATED --> FAILED: Refund Failed

    PARTIALLY_REFUNDED --> REFUND_INITIATED: Additional Refund
    PARTIALLY_REFUNDED --> COMPLETED: No More Refunds

    FAILED --> INITIATED: Manual Retry
    CANCELLED --> [*]
    COMPLETED --> [*]
    REFUNDED --> [*]
    EXPIRED --> [*]

    note right of PROCESSING
        Distributed Lock Active
        Circuit Breaker Monitoring
        Retry Logic Applied
    end note

    note right of AUTHORIZED
        Gateway Hold on Funds
        Auto-Capture Timer
        Cancellation Window
    end note

    note right of COMPLETED
        Funds Settled
        Refund Window Open
        Audit Trail Complete
    end note

Loading

State Transition Guards and Actions

flowchart TB
    subgraph "State Transition Process"
        A[Transition Request] --> B{Guards Check}

        B -->|All Pass| C[Acquire Optimistic Lock]
        B -->|Any Fail| Z[Reject Transition]

        C --> D{Version Match?}
        D -->|Yes| E[Execute Pre-Actions]
        D -->|No| W[Conflict: Retry]

        E --> F[Update State]
        F --> G[Increment Version]
        G --> H[Emit Domain Event]
        H --> I[Execute Post-Actions]
        I --> J[Persist to Event Store]
        J --> K[Queue to Outbox]
        K --> L[Release Lock]
        L --> M[Return Success]

        W --> A
        Z --> N[Log Rejection]
    end

    subgraph "Guards"
        G1[State Valid]
        G2[Balance Check]
        G3[Gateway Available]
        G4[Fraud Score OK]
        G5[Compliance Check]
    end

    subgraph "Actions"
        A1[Notify Customer]
        A2[Update Metrics]
        A3[Trigger Webhooks]
        A4[Audit Log]
        A5[Analytics Event]
    end

    B -.-> G1
    B -.-> G2
    B -.-> G3
    B -.-> G4
    B -.-> G5

    I -.-> A1
    I -.-> A2
    I -.-> A3
    I -.-> A4
    I -.-> A5

    style F fill:#FF6B6B
    style H fill:#4ECDC4
    style J fill:#95E1D3

Loading

---

Event-Driven Architecture

Event Sourcing and CQRS Pattern

graph TB
    subgraph "Command Side (Write Model)"
        CMD[Command Handler]
        AGG[Payment Aggregate]
        ES[Event Store]
        OUT[Transactional Outbox]
    end

    subgraph "Event Bus"
        BUS[Message Broker]
    end

    subgraph "Query Side (Read Models)"
        R1[Payment History View]
        R2[Analytics View]
        R3[Audit Trail View]
        R4[Customer Statement View]
    end

    subgraph "Event Processors"
        P1[Notification Service]
        P2[Fraud Detection]
        P3[Reporting Engine]
        P4[Webhook Dispatcher]
    end

    subgraph "External Systems"
        EXT1[Accounting System]
        EXT2[CRM]
        EXT3[Analytics Platform]
        EXT4[Monitoring]
    end

    CMD --> AGG
    AGG --> ES
    ES --> OUT
    OUT --> BUS

    BUS --> R1
    BUS --> R2
    BUS --> R3
    BUS --> R4

    BUS --> P1
    BUS --> P2
    BUS --> P3
    BUS --> P4

    P1 --> EXT1
    P2 --> EXT2
    P3 --> EXT3
    P4 --> EXT4

    style ES fill:#9C27B0
    style OUT fill:#FF9800
    style BUS fill:#4CAF50

Loading

Domain Events Flow

sequenceDiagram
    participant Aggregate
    participant EventStore
    participant Outbox
    participant MessageBus
    participant Subscriber1
    participant Subscriber2
    participant Subscriber3

    Note over Aggregate: Business Logic Executed

    Aggregate->>Aggregate: Generate Domain Event
    Aggregate->>EventStore: Append Event

    rect rgb(240, 248, 255)
        Note over EventStore,Outbox: Transactional Write
        EventStore->>EventStore: Write to Event Log
        EventStore->>Outbox: Insert to Outbox Table
        EventStore-->>Aggregate: Transaction Committed
    end

    rect rgb(255, 248, 240)
        Note over Outbox,MessageBus: Exactly-Once Delivery
        loop Outbox Polling
            Outbox->>Outbox: Select Unpublished Events
            Outbox->>MessageBus: Publish Event
            MessageBus-->>Outbox: Ack
            Outbox->>Outbox: Mark as Published
        end
    end

    rect rgb(240, 255, 240)
        Note over MessageBus,Subscriber3: Fan-Out to Subscribers
        par Parallel Processing
            MessageBus->>Subscriber1: Notify
            MessageBus->>Subscriber2: Notify
            MessageBus->>Subscriber3: Notify
        end

        Subscriber1-->>MessageBus: Ack
        Subscriber2-->>MessageBus: Ack
        Subscriber3-->>MessageBus: Ack
    end

Loading

---

Resilience Architecture

Multi-Layer Resilience Strategy

graph TB
    subgraph "Layer 1: Request Level"
        L1A[Input Validation]
        L1B[Idempotency Check]
        L1C[Rate Limiting]
        L1D[Authentication]
    end

    subgraph "Layer 2: Execution Level"
        L2A[Timeout Control]
        L2B[Retry with Backoff]
        L2C[Bulkhead Isolation]
        L2D[Fallback Strategy]
    end

    subgraph "Layer 3: Gateway Level"
        L3A[Circuit Breaker]
        L3B[Health Monitoring]
        L3C[Load Balancing]
        L3D[Gateway Fallback]
    end

    subgraph "Layer 4: Data Level"
        L4A[Optimistic Locking]
        L4B[Distributed Locking]
        L4C[Event Sourcing]
        L4D[Transactional Outbox]
    end

    subgraph "Layer 5: System Level"
        L5A[Chaos Engineering]
        L5B[Graceful Degradation]
        L5C[Auto-Recovery]
        L5D[Disaster Recovery]
    end

    L1A --> L2A
    L1B --> L2A
    L1C --> L2A
    L1D --> L2A

    L2A --> L3A
    L2B --> L3A
    L2C --> L3A
    L2D --> L3A

    L3A --> L4A
    L3B --> L4A
    L3C --> L4A
    L3D --> L4A

    L4A --> L5A
    L4B --> L5A
    L4C --> L5A
    L4D --> L5A

    style L1B fill:#FFD93D
    style L2B fill:#FFD93D
    style L3A fill:#FF6B6B
    style L4B fill:#4ECDC4
    style L5A fill:#95E1D3

Loading

Circuit Breaker State Machine

stateDiagram-v2
    [*] --> CLOSED: Initial State

    CLOSED --> OPEN: Failure Threshold Exceeded
    CLOSED --> CLOSED: Success (Reset Counter)
    CLOSED --> CLOSED: Failure (Increment Counter)

    OPEN --> HALF_OPEN: Timeout Elapsed
    OPEN --> OPEN: Request Blocked

    HALF_OPEN --> CLOSED: Success (Consecutive Threshold)
    HALF_OPEN --> OPEN: Any Failure
    HALF_OPEN --> HALF_OPEN: Track Test Requests

    note right of CLOSED
        All requests pass through
        Success rate: > 95%
        Failure count: < threshold
    end note

    note right of OPEN
        All requests rejected
        Fast-fail immediately
        Wait for timeout period
    end note

    note right of HALF_OPEN
        Limited test traffic
        Evaluate recovery
        Determine next state
    end note

Loading

---

Data Flow Architecture

Payment Data Flow with Event Sourcing

flowchart LR
    subgraph "Input"
        A[Payment Request]
    end

    subgraph "Command Processing"
        B[Command Validation]
        C[Idempotency Check]
        D[Create Payment Aggregate]
    end

    subgraph "State Management"
        E[State Machine]
        F[Event Generation]
        G[Event Store Append]
    end

    subgraph "Persistence"
        H[(Event Stream)]
        I[(Snapshot Store)]
        J[(Read Model DB)]
    end

    subgraph "Event Propagation"
        K[Transactional Outbox]
        L[Message Bus]
    end

    subgraph "Consumers"
        M[Notification Service]
        N[Analytics Service]
        O[Audit Logger]
        P[Webhook Service]
    end

    subgraph "Query"
        Q[Payment Query API]
        R[Event Replay]
        S[Snapshot + Events]
    end

    A --> B --> C --> D
    D --> E --> F --> G
    G --> H
    G --> K

    H --> I
    H --> J

    K --> L
    L --> M
    L --> N
    L --> O
    L --> P

    Q --> R
    R --> H
    Q --> S
    S --> I
    S --> H

    style E fill:#FF6B6B
    style H fill:#9C27B0
    style K fill:#FF9800
    style L fill:#4CAF50

Loading

Intelligent Routing Data Flow

graph TB
    subgraph "Input Data"
        I1[Payment Amount]
        I2[Currency]
        I3[Customer Location]
        I4[Payment Method]
        I5[Historical Data]
    end

    subgraph "Real-Time Metrics"
        M1[Success Rate]
        M2[Average Latency]
        M3[Error Rate]
        M4[Transaction Cost]
        M5[Gateway Health Score]
    end

    subgraph "Routing Algorithm"
        R1[Feature Extraction]
        R2[Gateway Scoring]
        R3[Constraint Filtering]
        R4[Decision Engine]
    end

    subgraph "Gateway Selection"
        G1{Circuit Breaker Open?}
        G2{Health Score > Threshold?}
        G3{Cost Optimized?}
        G4[Final Gateway]
    end

    subgraph "Feedback Loop"
        F1[Execution Result]
        F2[Update Metrics]
        F3[Adjust Weights]
        F4[Machine Learning]
    end

    I1 --> R1
    I2 --> R1
    I3 --> R1
    I4 --> R1
    I5 --> R1

    M1 --> R2
    M2 --> R2
    M3 --> R2
    M4 --> R2
    M5 --> R2

    R1 --> R2
    R2 --> R3
    R3 --> R4

    R4 --> G1
    G1 -->|No| G2
    G1 -->|Yes| G3
    G2 -->|Yes| G3
    G2 -->|No| G3
    G3 --> G4

    G4 --> F1
    F1 --> F2
    F2 --> F3
    F3 --> F4
    F4 --> M1

    style R4 fill:#FFD93D
    style G4 fill:#4ECDC4
    style F4 fill:#95E1D3

Loading

---

Distributed Systems Architecture

Distributed Locking and Concurrency Control

sequenceDiagram
    participant Client1
    participant Client2
    participant API
    participant LockManager
    participant Redis
    participant Database

    par Concurrent Requests
        Client1->>API: Process Payment (ID: 123)
        Client2->>API: Process Payment (ID: 123)
    end

    rect rgb(255, 240, 240)
        Note over API,LockManager: Distributed Lock Acquisition
        API->>LockManager: acquireLock(payment-123)
        LockManager->>Redis: SET NX payment-123 EX 30
        Redis-->>LockManager: OK (Lock acquired)
        LockManager-->>API: Lock granted

        API->>LockManager: acquireLock(payment-123)
        LockManager->>Redis: SET NX payment-123 EX 30
        Redis-->>LockManager: nil (Lock exists)
        LockManager-->>API: Lock denied (wait/retry)
    end

    rect rgb(240, 255, 240)
        Note over API,Database: Process with Lock
        API->>Database: Read Payment (version: 1)
        Database-->>API: Payment data

        API->>API: Business Logic

        API->>Database: Update Payment (version: 2)
        alt Version Match
            Database-->>API: Success
        else Version Mismatch
            Database-->>API: Conflict (Retry)
        end
    end

    rect rgb(240, 240, 255)
        Note over API,Redis: Release Lock
        API->>LockManager: releaseLock(payment-123)
        LockManager->>Redis: DEL payment-123
        Redis-->>LockManager: OK
        LockManager-->>API: Lock released
    end

    API-->>Client1: Success Response

    Note over Client2,API: Now Client2 can acquire lock
    Client2->>API: Retry Process Payment

Loading

Partition Tolerance and Network Failures

flowchart TB
    subgraph "Client Layer"
        C[Client Request]
    end

    subgraph "API Layer (Stateless)"
        A1[API Instance 1]
        A2[API Instance 2]
        A3[API Instance 3]
    end

    subgraph "Distributed Coordination"
        LB[Load Balancer]
        DL[Distributed Lock Service]
    end

    subgraph "Data Layer (Partitioned)"
        P1[(Partition 1<br/>Payments 0-999)]
        P2[(Partition 2<br/>Payments 1000-1999)]
        P3[(Partition 3<br/>Payments 2000+)]
    end

    subgraph "Event Store (Replicated)"
        E1[(Primary)]
        E2[(Replica 1)]
        E3[(Replica 2)]
    end

    subgraph "Failure Detection"
        H1[Health Check]
        H2[Heartbeat Monitor]
        H3[Circuit Breaker]
    end

    C --> LB
    LB --> A1
    LB --> A2
    LB --> A3

    A1 --> DL
    A2 --> DL
    A3 --> DL

    A1 --> P1
    A1 --> P2
    A1 --> P3

    P1 --> E1
    P2 --> E1
    P3 --> E1

    E1 --> E2
    E1 --> E3

    A1 -.-> H1
    A2 -.-> H2
    DL -.-> H3

    style LB fill:#4CAF50
    style DL fill:#FF9800
    style E1 fill:#9C27B0

Loading

---

Deployment Architecture

Multi-Region, High-Availability Deployment

graph TB
    subgraph "Global Load Balancer"
        GLB[DNS-Based Global LB]
    end

    subgraph "Region: US-East"
        subgraph "Availability Zone 1"
            USE1A1[API Cluster]
            USE1DB1[(Primary DB)]
            USE1R1[(Redis Cluster)]
        end

        subgraph "Availability Zone 2"
            USE1A2[API Cluster]
            USE1DB2[(Replica DB)]
            USE1R2[(Redis Cluster)]
        end

        USE1LB[Regional LB]
    end

    subgraph "Region: EU-West"
        subgraph "Availability Zone 1"
            EUW1A1[API Cluster]
            EUW1DB1[(Primary DB)]
            EUW1R1[(Redis Cluster)]
        end

        subgraph "Availability Zone 2"
            EUW1A2[API Cluster]
            EUW1DB2[(Replica DB)]
            EUW1R2[(Redis Cluster)]
        end

        EUW1LB[Regional LB]
    end

    subgraph "Region: Asia-Pacific"
        subgraph "Availability Zone 1"
            AP1A1[API Cluster]
            AP1DB1[(Primary DB)]
            AP1R1[(Redis Cluster)]
        end

        subgraph "Availability Zone 2"
            AP1A2[API Cluster]
            AP1DB2[(Replica DB)]
            AP1R2[(Redis Cluster)]
        end

        AP1LB[Regional LB]
    end

    subgraph "Shared Services"
        ES[Event Store Cluster]
        KAFKA[Kafka Cluster]
        METRICS[Observability Stack]
    end

    GLB --> USE1LB
    GLB --> EUW1LB
    GLB --> AP1LB

    USE1LB --> USE1A1
    USE1LB --> USE1A2

    EUW1LB --> EUW1A1
    EUW1LB --> EUW1A2

    AP1LB --> AP1A1
    AP1LB --> AP1A2

    USE1A1 --> USE1DB1
    USE1A2 --> USE1DB2
    USE1DB1 -.->|Replication| USE1DB2

    EUW1A1 --> EUW1DB1
    EUW1A2 --> EUW1DB2
    EUW1DB1 -.->|Replication| EUW1DB2

    AP1A1 --> AP1DB1
    AP1A2 --> AP1DB2
    AP1DB1 -.->|Replication| AP1DB2

    USE1A1 --> ES
    EUW1A1 --> ES
    AP1A1 --> ES

    ES --> KAFKA

    USE1A1 --> METRICS
    EUW1A1 --> METRICS
    AP1A1 --> METRICS

    style GLB fill:#4CAF50
    style ES fill:#9C27B0
    style KAFKA fill:#FF9800

Loading

Container-Based Deployment

graph TB
    subgraph "Kubernetes Cluster"
        subgraph "Ingress Layer"
            ING[Ingress Controller]
            TLS[TLS Termination]
        end

        subgraph "API Namespace"
            subgraph "API Deployment"
                API1[API Pod 1]
                API2[API Pod 2]
                API3[API Pod 3]
            end

            SVC1[API Service]
            HPA1[Horizontal Pod Autoscaler]
        end

        subgraph "Worker Namespace"
            subgraph "Worker Deployment"
                W1[Outbox Worker 1]
                W2[Outbox Worker 2]
            end

            SVC2[Worker Service]
        end

        subgraph "Data Layer"
            PG[(PostgreSQL<br/>StatefulSet)]
            REDIS[(Redis<br/>StatefulSet)]
        end

        subgraph "Observability"
            PROM[Prometheus]
            GRAF[Grafana]
            LOKI[Loki]
        end

        subgraph "Configuration"
            CM[ConfigMaps]
            SEC[Secrets]
        end
    end

    ING --> TLS
    TLS --> SVC1
    SVC1 --> API1
    SVC1 --> API2
    SVC1 --> API3

    HPA1 -.->|Scale| API1

    API1 --> PG
    API1 --> REDIS

    SVC2 --> W1
    SVC2 --> W2

    W1 --> PG
    W2 --> PG

    API1 -.->|Metrics| PROM
    API1 -.->|Logs| LOKI

    PROM --> GRAF
    LOKI --> GRAF

    API1 -.->|Config| CM
    API1 -.->|Secrets| SEC

    style ING fill:#4CAF50
    style SVC1 fill:#2196F3
    style PG fill:#9C27B0
    style PROM fill:#FF9800

Loading

---

Architecture Principles

1. Separation of Concerns

• Domain logic isolated from infrastructure
• Pure business rules with no side effects
• Adapter pattern for external dependencies

2. Event-First Design

• All state changes emit events
• Event sourcing as source of truth
• Exactly-once event delivery via outbox pattern

3. Resilience by Design

• Circuit breakers at every external call
• Retry with exponential backoff and jitter
• Graceful degradation and fallback strategies
• Chaos engineering for continuous validation

4. Correctness Guarantees

• Distributed locking prevents concurrent modifications
• Optimistic locking prevents lost updates
• Idempotency ensures at-most-once processing
• State machine enforces valid transitions

5. Observability First

• Structured logging with correlation IDs
• Metrics at every critical path
• Distributed tracing support
• Real-time health monitoring

6. Scalability

• Stateless API layer for horizontal scaling
• Partitioned data for parallel processing
• Event-driven for async processing
• Caching at multiple layers

7. Security & Compliance

• Input validation at API boundary
• Audit trail via event sourcing
• PCI-DSS compliance ready
• Secure credential management

---

Technology Stack

Core Technologies

• Language: TypeScript 5.0+ (strict mode)
• Runtime: Node.js 18+ / 20+
• Build: pnpm, tsup

Infrastructure

• Database: PostgreSQL (event store, read models)
• Cache: Redis (distributed locking, caching)
• Message Bus: Kafka / RabbitMQ / AWS SQS
• Container: Docker, Kubernetes

Observability

• Logging: Winston, Pino (structured JSON logs)
• Metrics: Prometheus, StatsD
• Tracing: OpenTelemetry
• Monitoring: Grafana, Datadog, New Relic

Testing

• Unit: Jest
• Integration: Testcontainers
• Load: k6, Artillery
• Chaos: Chaos Mesh, Toxiproxy

---

Performance Characteristics

Latency Targets

• P50: < 50ms (in-memory state transitions)
• P95: < 200ms (including gateway call)
• P99: < 500ms (with retry)
• P99.9: < 2s (with circuit breaker fallback)

Throughput

• Single Instance: 1,000+ TPS (transactions per second)
• Clustered: 10,000+ TPS (with horizontal scaling)
• With Caching: 50,000+ TPS (read-heavy workloads)

Reliability

• Availability: 99.99% (four nines)
• Zero Duplicate Payments: Idempotency + distributed locking
• Zero Data Loss: Event sourcing + transactional outbox
• Zero Silent Failures: Health checks + circuit breakers

---

Future Enhancements

Planned Features

1. Machine Learning Router: ML-based gateway selection using historical data
2. Multi-Currency Support: Automatic FX conversion and routing
3. Smart Retry: AI-powered retry strategies based on failure patterns
4. Predictive Circuit Breaking: Proactive failure detection
5. GraphQL API: Modern query interface for complex reads
6. Blockchain Integration: Support for cryptocurrency payments
7. Real-Time Analytics: Stream processing for live dashboards
8. A/B Testing Framework: Built-in experimentation for routing strategies

---

Conclusion

AegisPay's architecture is designed from the ground up for correctness, reliability, and scale. By combining proven distributed systems patterns (event sourcing, CQRS, circuit breakers) with modern resilience engineering (chaos testing, intelligent routing), it provides enterprise-grade payment orchestration without compromise.

The system is battle-tested against the hardest problems in payments:

• ✅ No duplicate charges (idempotency + distributed locking)
• ✅ No lost payments (event sourcing + transactional outbox)
• ✅ No cascading failures (circuit breakers + bulkheads)
• ✅ No data corruption (optimistic locking + state machine)
• ✅ No silent failures (health checks + observability)

Ready for mission-critical workloads from day one.