Distributed Notification Service

A scalable, multi-channel notification platform built with NestJS, PostgreSQL, Redis, BullMQ, and Prisma.

Features

• Multi-channel notification delivery
  • Email (Resend)
  • SMS (Twilio)
  • Push Notifications (Firebase Cloud Messaging)
  • In-App Notifications (Server-Sent Events)
• User notification preferences
• Notification history
• Read / Unread tracking
• Unread notification counts
• Priority-based processing
• Queue-driven architecture
• Delivery-level retries
• Real-time notifications using Server-Sent Events (SSE)
• Redis Pub/Sub for cross-instance event propagation
• Horizontal scaling support
• Nginx load balancing

Tech Stack

• NestJS
• TypeScript
• Prisma
• PostgreSQL
• Redis
• BullMQ
• Firebase Cloud Messaging (FCM)
• Server-Sent Events (SSE)
• Nginx
• Resend
• Twilio

Architecture

                        Nginx
                  (Load Balancer)
                             │
        ┌────────────────────┼────────────────────┐
        ▼                    ▼                    ▼
    NestJS #1           NestJS #2           NestJS #3
        │                    │                    │
        └────────────────────┼────────────────────┘
                             │
                          Redis
                  Pub/Sub + BullMQ
                             │
                    Notification API
                             │
                   Create Notification
                             │
                    Create Deliveries
                             │
                        Queue Router
                             │
      email-queue  sms-queue  push-queue  inapp-queue
            │          │           │            │
            ▼          ▼           ▼            ▼
      EmailWorker SMSWorker PushWorker InAppWorker
            │          │           │            │
            ▼          ▼           ▼            ▼
        Resend      Twilio       FCM          SSE

Current Progress

Core Platform

• Notification creation
• Delivery record creation
• User preferences
• Delivery tracking
• Priority handling
• Retry mechanism

In-App Notifications

• SSE-based real-time delivery
• Notification history
• Read / Unread state management
• Unread count tracking
• Redis Pub/Sub integration
• Multi-instance event delivery

Email

• Resend integration
• HTML email templates
• Provider response tracking

SMS

• Twilio integration
• Provider response tracking

Push Notifications

• Firebase Cloud Messaging (FCM) integration
• Browser push notifications
• Device token registration
• Push token persistence
• Worker-based push delivery
• Provider response tracking

Infrastructure

• Redis integration
• BullMQ queue processing
• Dedicated workers per channel
• Horizontal scaling support
• Nginx reverse proxy and load balancing
• SSE proxy optimization

Notification Flow

Client
   │
   ▼
Notification API
   │
   ▼
Create Notification
   │
   ▼
Create Deliveries
   │
   ▼
Queue Router
   │
   ├── Email Queue
   ├── SMS Queue
   ├── Push Queue
   └── In-App Queue
            │
            ▼
         Workers
            │
            ▼
        Providers
            │
            ▼
Resend | Twilio | FCM | SSE

Next

• Rate Limiting
• Delivery Metrics
• Observability & Monitoring