Sure! Here’s a clear and practical explanation of Real-Time Notification Systems using Pub/Sub and Firebase, including key concepts, architecture, and how to implement it.

🟢 Real-Time Notification Systems with Pub/Sub and Firebase

Real-time notification systems are essential for modern applications—whether it's alerting users about messages, updates, transactions, or other events. Using Google Cloud Pub/Sub and Firebase, you can build a scalable, real-time notification system.

🔧 Technologies Used

Google Cloud Pub/Sub

A messaging service for exchanging event data between independent services.

Handles asynchronous event-driven architectures.

Firebase Cloud Messaging (FCM)

A cross-platform service to send push notifications to Android, iOS, and web clients.

Integrated with Firebase Authentication, Firestore, and more.

Cloud Functions (GCP/Firebase Functions)

Serverless functions that run in response to events (like a Pub/Sub message or Firestore write).

Perfect for reacting to backend events and triggering notifications.

🏗️ Architecture Overview

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[Client Action] --> [API / Backend Service] 

        --> Publishes Message to --> [Pub/Sub Topic] 

        --> Triggers --> [Cloud Function Subscriber] 

        --> Sends Notification via --> [Firebase Cloud Messaging]

        --> [User Device Receives Push Notification]

🧱 Implementation Steps

1. Create a Pub/Sub Topic

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gcloud pubsub topics create notify-users

2. Publish Messages to the Topic

Your backend service (Node.js, Python, etc.) can publish messages when an event occurs:

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const {PubSub} = require('@google-cloud/pubsub');

const pubSubClient = new PubSub();

const publishMessage = async (data) => {

  const dataBuffer = Buffer.from(JSON.stringify(data));

  await pubSubClient.topic('notify-users').publish(dataBuffer);

};

3. Subscribe with a Cloud Function

Create a function that listens to notify-users topic:

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exports.sendNotification = functions.pubsub.topic('notify-users').onPublish(async (message) => {

  const data = message.json;

  const { userId, title, body } = data;

  const userToken = await getUserFcmToken(userId); // from Firestore or Realtime DB

  const payload = {

    notification: { title, body },

    token: userToken,

  };

  await admin.messaging().send(payload);

});

4. Manage FCM Tokens on the Client

Make sure your client app stores the FCM token in Firestore or Realtime Database upon login or token refresh.

Example (Web using Firebase JS SDK):

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messaging.getToken({ vapidKey: 'YOUR_VAPID_KEY' }).then((currentToken) => {

  if (currentToken) {

    // Send token to your backend or store in Firestore

  }

});

🔐 Security & Best Practices

Secure FCM tokens: Only send to authenticated users and avoid leaking tokens.

Rate limits & retries: Pub/Sub and FCM both handle retries, but monitor them.

Topic filtering: You can filter notifications per topic (e.g., news-updates, chat-messages).

✅ Use Cases

Chat applications (new message alerts)

E-commerce platforms (order updates, shipment tracking)

Social networks (likes, comments, follows)

News apps (breaking news alerts)

🚀 Benefits

Scalability: Pub/Sub handles millions of messages per second.

Real-time: Firebase ensures instant delivery to end-users.

Decoupled architecture: Backend services remain loosely coupled and independently scalable.

Learn Google Cloud Data Engineering Course

Read More

Replay Mechanisms and Dead Letter Topics in Cloud Pub/Sub

Designing an Event-Driven Architecture for Microservices with Pub/Sub

Building a Fan-out Architecture with Cloud Pub/Sub and Cloud Functions

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