GopherPay

The goal is to build a distributed system that handles user accounts, money transfers, and transaction history.

System Architecture

Instead of one big application, we will split the logic into three core services:

• Identity Service: Manages user registration, profiles, and authentication (JWT).
• Account Service: Manages bank accounts, wallet balances, and currency types.
• Transaction Service: Handles the logic of moving money from Wallet A to Wallet B (The "Engine").

Utility/Support Service:

• Nottification Service (Novu): A dedicated, asynchronous support service responsible for managing all outgoing communications between the system and its users

Infrastructures:

• Message Broker (Apache Kafka): The asynchronous backbone that decouples the core services from the support services

Core Service Breakdown

Service A: Identity & Auth

• Focus: Security and Middleware.
• Key Tasks:
  • POST /auth/register
  • POST /auth/login.
• Use Bcrypt for password hashing.
• Generate JWT (JSON Web Tokens) for authenticated requests.

Service B: Account Management

• Focus: CRUD operations and Database design.
• Key Tasks:
  • GET /accounts/me: Fetch current balance.
  • POST /accounts: Create a new currency wallet (e.g., USD, VND).
  • GET /accounts/me: Fetch current balance.
  • POST /accounts: Create a new currency wallet (e.g., USD, VND).

Service C: Transaction Engine (The Core)

• Focus: Concurrency and Atomicity.
• Key Tasks: POST /transfer: Transfer money between users.
• Crucial Concept: Using Database Transactions to ensure that if the sender's deduction fails, the receiver's credit never happens.

Security

The most secure way is to use the openssl tool, which is pre-installed on Linux, macOS, and Git Bash for Windows.

• For JWT_SECRET: Run this to get a long random string:

openssl rand -base64 32

• For STORE_ENCRYPTION_KEY: Run this to get exactly 32 hex characters:

openssl rand -hex 16

Connecting Separate Docker Compose Projects

Create the Shared Network

1. Create a global network that exists outside of any specific docker-compose.yml file. Open terminal (PowerShell) and run:

docker network create gopher_network

2. Verify it exists by running

docker network ls

Update the Docker Compose Files

Tell each service to join this external network. Add the networks configuration to the kafka_connect (and all other services) service and define the network at the bottom.

services:
  kafka_connect:
    # ... existing config ...
    networks:
      - gopher_net

networks:
  gopher_net:
    external: true
    name: gopher_network

Restart Services

Navigate to each directory and restart the containers to apply the network changes:

docker compose up -d

Verification

1. Check if both containers have successfully joined the "bridge":

docker network inspect gopher_network

2. Look for the Containers section. You should see all services listed there with their internal IPs.