saga-pattern

An example implementation of the saga pattern in Go using microservices architecture.

Architecture

This project consists of three microservices that implement a distributed saga pattern for a mortgage loan system:

• Service 1 (port 8081): Customer Service - manages customer information
• Service 2 (port 8082): Mortgage Application Service - handles mortgage applications
• Service 3 (port 8083): Loan Servicing Service - manages active loans and payments

All services share a single PostgreSQL database server but use separate databases (schemas):

• service1_db - Customer database
• service2_db - Mortgage application database
• service3_db - Loan servicing database

Quick Start

Prerequisites

• Docker and Docker Compose installed
• Ports 5432, 8081, 8082, 8083 available

Running All Services

From the project root directory:

# Build and start all services
docker-compose up --build

# Or run in detached mode
docker-compose up -d --build

This will:

1. Start a PostgreSQL server on port 5432
2. Create three separate databases (service1_db, service2_db, service3_db)
3. Build and start all three Go services
4. Set up networking between services

Stopping Services

# Stop all services
docker-compose down

# Stop and remove volumes (clears database data)
docker-compose down -v

Viewing Logs

# View all logs
docker-compose logs

# View logs for a specific service
docker-compose logs service1
docker-compose logs service2
docker-compose logs service3
docker-compose logs postgres

# Follow logs in real-time
docker-compose logs -f

API Endpoints

Service 1 - Customer Service (port 8081)

• POST /customers - Create customer
• GET /customers/:id - Get customer by ID
• PUT /customers/:id - Update customer
• DELETE /customers/:id - Delete customer

Service 2 - Mortgage Application Service (port 8082)

• POST /applications - Create mortgage application
• GET /applications/:id - Get application by ID
• PUT /applications/:id - Update application (approve/reject)
• DELETE /applications/:id - Delete application
• GET /customers/:customerId/applications - Get all applications for a customer

Service 3 - Loan Servicing Service (port 8083)

• POST /loans - Create loan
• GET /loans/:id - Get loan by ID
• PUT /loans/:id - Update loan
• DELETE /loans/:id - Delete loan
• GET /customers/:customerId/loans - Get all loans for a customer
• GET /mortgages/:mortgageId/loan - Get loan by mortgage ID
• POST /payments - Create payment
• GET /payments/:id - Get payment by ID
• GET /loans/:loanId/payments - Get all payments for a loan
• GET /customers/:customerId/payments - Get all payments for a customer

Testing

Use the test-client.http files in each service directory to test the APIs with your HTTP client.

Database Access

Connect to the PostgreSQL database:

# Using docker exec
docker exec -it saga_postgres psql -U postgres -d service1_db
docker exec -it saga_postgres psql -U postgres -d service2_db
docker exec -it saga_postgres psql -U postgres -d service3_db

# From host (if psql is installed)
psql -h localhost -U postgres -d service1_db

Default credentials:

• Username: postgres
• Password: postgres

Development

Running Individual Services Locally

Each service can be run independently for development:

# Start only the database
docker-compose up postgres

# Run service locally (example for service1)
cd service1/api
go run main.go

Make sure to update the DATABASE_URL in each service's .env file if running locally.

Project Structure

saga-pattern/
├── docker-compose.yml          # Main orchestration file
├── init-db.sql                 # Database initialization script
├── service1/                   # Customer service
│   ├── Dockerfile
│   ├── docker-compose.yml      # Individual service compose file
│   ├── api/
│   └── ...
├── service2/                   # Mortgage application service
│   ├── Dockerfile
│   ├── docker-compose.yml
│   ├── api/
│   └── ...
└── service3/                   # Loan servicing service
    ├── Dockerfile
    ├── docker-compose.yml
    ├── api/
    └── ...