System Design FAQ: Top Questions

A Notification System delivers messages to users via various channels like email, SMS, push, or in-app alerts. It must be reliable, scalable, and capable of handling retries and failures.

📋 Functional Requirements

• Send alerts via multiple channels (email, SMS, push)
• Support templating and personalization
• Track delivery status and failures
• Provide retry logic and backoff strategies

📦 Non-Functional Requirements

• High availability and low latency
• Message deduplication and idempotency
• Secure handling of user PII

🏗️ Architecture Overview

• Frontend/API Gateway: Triggers notification
• Notification Service: Core logic, templates, scheduling
• Channel Workers: Separate workers for Email, SMS, Push
• Queue: Kafka/SQS to decouple producers and consumers
• Audit Store: For delivery logs and analytics

🔧 Email Notification (Node.js + SendGrid)

const sgMail = require('@sendgrid/mail');
sgMail.setApiKey(process.env.SENDGRID_API_KEY);

const msg = {
  to: 'user@example.com',
  from: 'no-reply@myapp.com',
  subject: 'Welcome!',
  text: 'Thanks for signing up!',
  html: 'Thanks for signing up!',
};

sgMail.send(msg).then(() => {
  console.log('Email sent');
}).catch((error) => {
  console.error(error);
});
        

📱 SMS Notification (Python + Twilio)

from twilio.rest import Client

client = Client("ACXXXX", "your_auth_token")
message = client.messages.create(
    body="Your OTP is 123456",
    from_="+1234567890",
    to="+19876543210"
)
print(message.sid)
        

📲 Push Notification (Firebase FCM)

const admin = require('firebase-admin');
admin.initializeApp();

const payload = {
  notification: {
    title: "Reminder",
    body: "You have a meeting at 10 AM"
  }
};

admin.messaging().sendToDevice(deviceToken, payload)
  .then(response => console.log("Push sent:", response))
  .catch(err => console.error("Push error:", err));
        

🧪 Delivery Tracking Table (SQL)

CREATE TABLE notifications (
    id UUID PRIMARY KEY,
    user_id UUID,
    channel VARCHAR(10), -- email, sms, push
    status VARCHAR(20),  -- pending, delivered, failed
    created_at TIMESTAMP DEFAULT NOW(),
    sent_at TIMESTAMP,
    error TEXT
);
        

⏱️ Retry Strategy

• Exponential backoff with jitter
• Dead letter queue for unprocessed notifications
• Cap retries to avoid infinite loops

☁️ Cloud Providers

• Email: AWS SES, SendGrid, Postmark
• SMS: Twilio, AWS SNS
• Push: Firebase Cloud Messaging (FCM), OneSignal

🧠 Scaling Considerations

• Batch processing for high throughput (Kafka consumers)
• Rate limits from 3rd-party APIs must be respected
• Use region-based workers for low latency

📌 Final Insight

A notification system is a cross-cutting concern in many systems. Abstracting delivery logic, using queues, and isolating channels help build resilient, testable infrastructure with observability.