FlashSend — Distributed Notification Platform

FlashSend is a Go-based distributed notification delivery system designed to reliably send SMS, Email, and scheduled notifications at scale. It uses a RabbitMQ-powered asynchronous worker architecture with retries, dead-letter queues (DLQ), DB-backed scheduling, and automatic SMS provider failover (Twilio → Vonage) to guarantee delivery even during traffic spikes and third-party outages.

Features

• Send SMS and Email notifications
• Schedule notifications for future delivery
• RabbitMQ asynchronous processing
• Exponential retry pipelines
• Dead Letter Queues (DLQ) for fault isolation
• Automatic SMS provider failover (Twilio → Vonage)
• Horizontally scalable distributed workers
• JWT authentication & API-key based access
• PostgreSQL-backed persistence
• Status-driven notification lifecycle
• Human-readable 24-hour time scheduling

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System Flow

Client → API (Gin) → RabbitMQ Queue → Distributed Workers → Providers (SMS/Email)
                                  ↘ DLQ (failed messages)

Scheduled notifications are stored in PostgreSQL and scanned by a cron-like scheduler built using Go’s time.Ticker.

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⚙ Tech Stack

Layer	Technology
Language	Go
API Framework	Gin
Queue	RabbitMQ
Database	PostgreSQL
SMS Providers	Twilio, Vonage
Auth	JWT
Scheduler	Goroutines + time.Ticker

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Notification Lifecycle

queued → processing → retrying → sent → dead

Retries use exponential backoff. Notifications that exceed retry limits are routed to DLQ.

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Setup

1️⃣ Clone Repository

git clone https://github.com/TanishValesha/FlashSend-Notifier
cd FlashSend-Notifier

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2️⃣ Environment Variables

Create a .env file:

BIND_ADDR=:8080

JWT_SECRET=your-jwt-secret
APIKEY_HMAC_SECRET=your-apikey-secret
JWT_EXPIRATION_HOURS=24

DATABASE_URL=postgres://user:password@localhost:5432/flashsend?sslmode=disable

SMTP_HOST=smtp.gmail.com
SMTP_PORT=587
SMTP_EMAIL=your-email@gmail.com
SMTP_APP_PASSWORD=your-smtp-app-password

TWILIO_ACCOUNT_SID=your_twilio_sid
TWILIO_AUTH_TOKEN=your_twilio_auth_token
TWILIO_PHONE_NUMBER=your_twilio_phone

VONAGE_API_KEY=your_vonage_api_key
VONAGE_API_SECRET=your_vonage_api_secret
VONAGE_FROM=FlashSend

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3️⃣ Start Dependencies

docker-compose up -d postgres rabbitmq

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4️⃣ Run Server

go run ./cmd/server/main.go

5️⃣ Run Workers

go run ./cmd/worker/main.go

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API Documentation

Authentication APIs

Register

POST /api/auth/register

{
  "email": "user@example.com",
  "password": "password123"
}

Response

{
  "message": "User registered successfully"
}

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Login

POST /api/auth/login

{
  "email": "user@example.com",
  "password": "password123"
}

Response

{
  "token": "<jwt-token>"
}

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API Key Management

Create API Key

POST /api/apikeys

Response

{
  "key": "fs_98af3c1..."
}

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List API Keys

GET /api/apikeys

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Delete API Key

DELETE /api/apikeys/:id

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Send Notification

Send Instant Notification

POST /api/notify/send

{
  "channel": "sms",
  "to": "+919999999999",
  "subject": "optional for email",
  "body": "Hello from FlashSend"
}

Response

{
  "message": "Notification queued",
  "id": 12
}

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Schedule Notification

Schedule Notification

POST /api/notify/schedule

{
  "channel": "sms",
  "to": "+919999999999",
  "subject": "optional",
  "body": "Reminder",
  "scheduleAt": "2025-02-20 18:30"
}

Response

{
  "message": "Scheduled notification created",
  "id": 34
}

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Notification History

List Notifications

GET /api/notifications

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Get Single Notification

GET /api/notifications/:id

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Health Check

GET /ping

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Why FlashSend?

FlashSend demonstrates real-world distributed systems design patterns such as:

• Competing consumer worker pools
• Queue-based backpressure handling
• Fault-tolerant retry pipelines
• Scheduled job orchestration
• Provider failover and resiliency design