cephid

A distributed user registration system with event-driven architecture.

High-Level Overview

Flow:

1. User Registration – The user submits a registration form on the Frontend (Next.js)
2. Server Action – The browser invokes the registerUser() Server Action which returns a JSON response
3. gRPC Communication – The Next.js server communicates with the Backend (Spring) over a gRPC channel using binary protocol
4. Event Publishing – The backend produces a user_registered event to Kafka
5. Event Consumption – The Notification Service (Go) consumes messages from the Kafka topic
6. Email Delivery – The notification service sends a welcome email via Resend

Demo

Ping Test (gRPC health check):

Successful Registration:

Duplicate Email Validation:

Kafka UI – Events Published:

Welcome Email Received:

Ports

Service	Port	URL
Frontend	3000	http://localhost:3000
Backend (gRPC)	9090	localhost:9090
Kafka (host)	29094	localhost:29094
Kafka (internal)	9094	cephid-kafka:9094
Kafka UI	8080	http://localhost:8080
Notification Service	-	(Kafka consumer, no exposed port)

Environment Variables

Variable	Service	Description
RESEND_API_KEY	notification-service	Resend API key for sending emails

Running

Prerequisites:

• Docker and Docker Compose installed
• Resend API key (get one at resend.com)

1. Configure environment:

Create notification-service/.env file:

RESEND_API_KEY=re_xxxxxxxxx

2. Start all services:

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

3. Access the application:

Service	URL
Frontend	http://localhost:3000
Kafka UI	http://localhost:8080

Useful commands:

# Start in detached mode
docker-compose up -d --build

# View logs
docker-compose logs -f

# View logs for specific service
docker-compose logs -f frontend
docker-compose logs -f backend
docker-compose logs -f notification-service

# Stop all services
docker-compose down

# Stop and remove volumes (clean slate)
docker-compose down -v