🚀 Go Microservices E-Commerce Platform

Welcome to my journey of building a scalable microservices architecture using Golang! This project will implement core microservices patterns with modern technologies.

🌟 Key Features

• Event-Driven Architecture with Kafka & RabbitMQ
• Database Sharding with PostgreSQL Cluster
• Observability with OpenTelemetry & Grafana Stack
• Production-Grade Infrastructure Setup

🏗 Architecture Overview

graph TD
  A[Client] --> B[API Gateway]
  subgraph Core Services
    B --> C[Auth Service]
    B --> D[Product Service]
    B --> E[Order Service]
    B --> F[Mail Service]
  end

  subgraph Data Layer
    C --> G[PostgreSQL Cluster]
    D --> H[PostgreSQL Cluster]
    E --> I[PostgreSQL Cluster]
    E --> J[Redis Cluster]
  end

  subgraph Event Bus
    D --> K[Kafka Cluster]
    E --> K
    C --> L[RabbitMQ Cluster]
    F --> L
  end

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🛠 Service Breakdown

1. 🔐 Auth Service

Responsibilities: User identity management and authentication

sequenceDiagram
  participant Client
  participant Gateway
  participant AuthService
  participant PostgreSQL
  participant RabbitMQ

  Client->>Gateway: POST /register
  Gateway->>AuthService: Forward request
  AuthService->>PostgreSQL: Create user (unverified)
  AuthService->>RabbitMQ: Publish verification event
  RabbitMQ->>MailService: Consume event
  MailService->>User: Send verification email

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Key Features:

• JWT-based authentication
• Email verification with 10-minute expiry
• Anti-spam protection (1-minute cooldown)
• CQRS pattern with master-slave replication
• Horizontal scaling with pgpool-II

---

2. 📦 Product Service

Responsibilities: Product lifecycle management

graph TD
  A[Create Product] --> B[Kafka: product-created]
  C[Update Product] --> D[Kafka: product-updated]
  E[Order Created Event] --> F[Reduce Stock]
  B --> G[Order Service]
  D --> G

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Key Features:

• Real-time inventory synchronization
• Event sourcing for product changes
• CQRS pattern with master-slave replication

---

3. 🛒 Order Service

Responsibilities: Order processing and fulfillment

graph TD
  A[Order Created] --> B[Schedule Reminders]
  A --> C[Start 24h Countdown]
  B --> D[4h Reminder]
  B --> E[12h Reminder]
  B --> F[22h Reminder]
  C --> G[Expiration Check]

  D --> H[Send Email via Mail Service]
  E --> H
  F --> H
  G --> I{Payment Status?}

  I -->|Paid| J[Mark Order Completed]
  I -->|Unpaid| K[Cancel Order]
  K --> L[Restock Inventory]
  K --> M[Send Cancellation Email]

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1. Order Creation with Delayed Messages

sequenceDiagram
  participant Client
  participant Gateway
  participant OrderService
  participant PostgreSQL
  participant RabbitMQ
  participant Kafka

  Client->>Gateway: POST /orders
  Gateway->>OrderService: Forward request
  OrderService->>Redis: SETNX lock:request_id
  Redis-->>OrderService: Lock acquired
  OrderService->>PostgreSQL: Create order (status=PENDING)
  OrderService->>RabbitMQ: Publish delayed messages
  Note over RabbitMQ: 4h, 12h, 22h delays
  OrderService->>Kafka: order.created
  OrderService->>Redis: DEL lock:request_id
  Kafka->>ProductService: Reserve stock

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2. Payment Reminder Execution Flow

sequenceDiagram
  participant RabbitMQ
  participant OrderService
  participant PostgreSQL
  participant MailService

  RabbitMQ->>OrderService: Reminder event
  OrderService->>PostgreSQL: Get order status
  alt Status = PENDING
    OrderService->>MailService: Send payment reminder
    MailService->>User: Email reminder
  else Status = PAID/CANCELLED
    OrderService->>RabbitMQ: Acknowledge message
  end

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3. Order Expiration Handling

sequenceDiagram
  participant RabbitMQ
  participant OrderService
  participant PostgreSQL
  participant Kafka
  participant ProductService

  RabbitMQ->>OrderService: Expiration event (24h)
  OrderService->>PostgreSQL: Check payment status
  alt Unpaid
    OrderService->>PostgreSQL: Update status=CANCELLED
    OrderService->>Kafka: order.cancelled
    Kafka->>ProductService: Restock items
    OrderService->>MailService: Notify cancellation
  else Paid
    OrderService->>PostgreSQL: Update status=COMPLETED
  end

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🧠 Key Design Decisions

1. Delayed Message Implementation

   graph LR
     A[Order Service] -->|Publish with delay| B[RabbitMQ]
     B -->|x-delayed-message plugin| C[Delayed Exchange]
     C -->|TTL 4h| D[Reminder Queue]
     C -->|TTL 12h| E[Reminder Queue]
     C -->|TTL 22h| F[Reminder Queue]
     C -->|TTL 24h| G[Expiration Queue]
   

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2. State Transition Diagram

   stateDiagram-v2
     [*] --> PENDING
     PENDING --> PAID: Payment received
     PENDING --> CANCELLED: 24h timeout
     PAID --> COMPLETED: Order fulfilled
     CANCELLED --> [*]
     COMPLETED --> [*]
   

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Key Features:

• Redis distributed locking for idempotency
• Event-driven order processing
• Delayed message handling with RabbitMQ
• State transition management with PostgreSQL

---

4. 📧 Mail Service

Responsibilities: Asynchronous email processing

Key Features:

• RabbitMQ consumer
• Template-based email rendering
• Send retry mechanism with exponential backoff
• MailHog integration for development

---

5. 🌉 API Gateway

Responsibilities: Unified API entrypoint

Key Features:

• JWT validation middleware
• Rate limiting per service
• Request/Response transformation
• Prometheus metrics collection

🏭 Infrastructure Architecture

graph TD
  subgraph Database Layer
    A[PostgreSQL Cluster] --> B[Auth DB]
    A --> C[Product DB]
    A --> D[Order DB]
    B --> E[1 Master + 2 Replicas]
    C --> F[1 Master + 2 Replicas]
    D --> G[1 Master + 2 Replicas]
  end

  subgraph Message Brokers
    H[RabbitMQ Cluster] --> I[3 Nodes]
    J[Kafka Cluster] --> K[3 Brokers]
  end

  subgraph Caching
    L[Redis Cluster] --> M[3 Masters + 3 Replicas]
  end

  subgraph Observability
    N[Prometheus]
    O[Loki]
    P[Tempo]
    Q[Grafana]
    R[OpenTelemetry]
  end

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🔍 Observability Stack

graph TD
  A[Services] --> B[OpenTelemetry]
  B --> C[Metrics]
  B --> D[Traces]
  B --> E[Logs]
  C --> F[Prometheus]
  D --> G[Tempo]
  E --> H[Loki]
  F --> I[Grafana]
  G --> I
  H --> I

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Monitoring Features:

• Real-time service metrics
• Distributed tracing across services
• Centralized logging with labels
• Performance dashboards per service

🛠️ Technology Stack

Languages & Frameworks

• Go 1.23+
• Gin Web Framework

Databases

• PostgreSQL 16 with pgpool-II
• Bitnami Redis Latest Cluster

Message Brokers

• Bitnami Kafka Latest Cluster
• RabbitMQ 4.0 Cluster

Infrastructure

• Docker Swarm
• HAProxy for load balancing
• MailHog SMTP server

Observability

• Prometheus
• Grafana
• Loki
• Tempo
• OpenTelemetry

📈 Deployment Architecture

graph TD
  A[Load Balancer] --> B[API Gateway Cluster]
  B --> C[Auth Service Cluster]
  B --> D[Product Service Cluster]
  B --> E[Order Service Cluster]
  B --> F[Mail Service Cluster]

  C --> G[PostgreSQL Cluster]
  D --> H[PostgreSQL Cluster]
  E --> I[PostgreSQL Cluster]
  E --> J[Redis Cluster]

  C --> K[RabbitMQ Cluster]
  D --> L[Kafka Cluster]
  E --> L
  F --> K

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