How Realtime Chat Apps are? Know the Trade-Offs..

Real-time chat applications are everywhere—think WhatsApp, Slack, or Discord and soon my new Project NyayVaad. If you’ve built a basic chat app with Next.js and React, perhaps just an input form sending messages, you’re ready to make it robust, scalable, and feature-rich. This guide takes you from the fundamentals of what a chat app is to implementing WebSockets, managing sessions, storing messages, and ensuring reliability with backup queues. Written for beginners and seasoned developers alike, we’ll use a story-based approach to explore real-world scenarios, with minimal code to keep things clear and engaging. This is more of a practical approach and architectural overview than a guide.

1. What is a Chat App and How Should It Behave?

A chat application lets users send and receive messages instantly, mimicking a real-life conversation. Imagine you’re chatting with a friend on Discord: you type a message, hit send, and it appears on their screen in a split second. A great chat app should:

• Feel Instant: Messages arrive without delay, creating a smooth conversation flow.
• Be Reliable: Messages are never lost, even if you refresh the page or lose your internet connection.
• Offer Features: Show message history, typing indicators (“User is typing…”), read receipts, and who’s online.
• Work at Scale: Handle a handful of users or thousands without crashing.
• Be Intuitive: Provide a clean interface that works on phones, tablets, and desktops, with clear error messages (e.g., “You’re offline”).

The Reality of “Real-Time” Chat Apps

“Real-time” sounds magical, but it’s not instant like a video game or stock trading system. Chat apps tolerate slight delays (50-200ms) because humans don’t notice them. Technologies like WebSockets make this possible, but network issues, server load, or slow browsers can add tiny lags.

For New Developers:

• Small Apps: A chat for 10-50 users can run on one server with WebSockets and a simple database. It’s manageable for beginners.
• Big Apps: Apps like Slack handle millions of users with complex setups—multiple servers, databases, and queues. This is advanced and not needed for most projects.
• Challenges: New devs often struggle with keeping messages in sync, handling page refreshes, or scaling WebSockets. Start simple and add features step-by-step.

2. Introduction to WebSockets: Your First Chat App

WebSockets are the backbone of real-time apps. Unlike HTTP, where the browser asks the server for data, WebSockets keep an open connection so the server can push messages instantly. This makes them perfect for chat apps.

Why WebSockets?

• Fast: Messages arrive in real time without constant server requests.
• Efficient: One connection handles all communication, unlike polling (repeatedly asking the server for updates).
• Scalable: With the right setup, supports many users at once.

Let’s build a super simple chat app using Next.js, React, and Socket.IO. The goal: send a message from one browser and see it in another instantly. We’ll keep code minimal to focus on the concept.

Setting Up Your First WebSocket Chat App

Step 1: Create a Next.js Project

npx create-next-app@latest my-chat-app
cd my-chat-app
npm install socket.io socket.io-client

Step 2: Set Up the WebSocket Server

Create an API route to start a Socket.IO server that broadcasts messages.

// pages/api/socket.js
import { Server } from 'socket.io';

export default function handler(req, res) {
  if (!res.socket.server.io) {
    console.log('Starting WebSocket server...');
    const io = new Server(res.socket.server);
    io.on('connection', (socket) => {
      console.log('Client connected:', socket.id);
      socket.on('send_message', (msg) => {
        io.emit('receive_message', msg); // Send to all clients
      });
    });
    res.socket.server.io = io;
  }
  res.end();
}

Step 3: Build the Chat Component

Create a React component to connect to the server, send messages, and show received ones.

// components/Chat.js
import { useEffect, useState } from 'react';
import io from 'socket.io-client';

export default function Chat() {
  const [message, setMessage] = useState('');
  const [receivedMessages, setReceivedMessages] = useState([]);
  let socket;

  useEffect(() => {
    socket = io('http://localhost:3000');
    socket.on('receive_message', (msg) => {
      setReceivedMessages((prev) => [...prev, msg]);
    });
    return () => socket.disconnect();
  }, []);

  const sendMessage = () => {
    if (message.trim()) {
      socket.emit('send_message', message);
      setMessage('');
    }
  };

  return (
    <div style={{ padding: '20px' }}>
      <h1>Simple Chat</h1>
      <div>
        {receivedMessages.map((msg, index) => (
          <p key={index}>{msg}</p>
        ))}
      </div>
      <input
        type="text"
        value={message}
        onChange={(e) => setMessage(e.target.value)}
        placeholder="Type a message..."
        style={{ marginRight: '10px' }}
      />
      <button onClick={sendMessage}>Send</button>
    </div>
  );
}

Step 4: Initialize the WebSocket Server

Ensure the server starts when the app loads.

// pages/_app.js
import { useEffect } from 'react';
import '../styles/globals.css';

function MyApp({ Component, pageProps }) {
  useEffect(() => {
    fetch('/api/socket');
  }, []);
  return <Component {...pageProps} />;
}

export default MyApp;

Step 5: Update the Home Page

Use the Chat component on the home page.

// pages/index.js
import Chat from '../components/Chat';

export default function Home() {
  return <Chat />;
}

Step 6: Run the App

npm run dev

Open two browser tabs at http://localhost:3000. Type a message in one tab, click “Send,” and see it appear in both tabs instantly. You’ve just built a real-time chat app!

How It Works

• The server (/api/socket) sets up Socket.IO and listens for send_message events.
• When you send a message, the server broadcasts it to all clients via receive_message.
• The React component connects to the server, listens for messages, and updates the UI.

This is a starting point. It doesn’t save messages or track users yet, but it shows WebSockets in action.

3. Key Considerations for WebSockets in Next.js

Using WebSockets with Next.js requires careful planning. Here are five key points to consider:

1. Serverless vs. Custom Server:

• Next.js API routes are serverless, which can disrupt WebSocket connections. Our example uses a persistent server, but scaling may require a custom Node.js server.
• Trade-Off: Serverless is cheap and easy but less suited for WebSockets; a custom server offers control but needs more maintenance.

1. Scaling WebSockets:

• WebSockets keep connections open, which can overload a single server. Use a Redis adapter with Socket.IO to sync messages across multiple servers.
• Trade-Off: Redis enables scaling but adds setup complexity.

1. Security:

• Use WSS (WebSocket Secure) with SSL/TLS to encrypt data. Add JWT authentication to verify users and rate-limit messages to prevent spam.
• Trade-Off: Security is essential but increases development time.

1. Error Handling:

• Handle dropped connections, network issues, or server restarts. Socket.IO’s reconnection feature helps, but you’ll need to resync messages on reconnect.
• Trade-Off: Robust error handling improves user experience but adds code.

1. Performance:

• Compress messages and limit event frequency to save bandwidth. Monitor server resources (CPU/memory) under load.
• Trade-Off: Optimization boosts efficiency but requires testing to avoid over-engineering.

4. Do You Need WebSockets for a Chatbot?

If your chat app includes a chatbot (e.g., an AI replying to messages), you might wonder if WebSockets are necessary. Let’s explore:

• HTTP Call-Response:

  • Send a user’s message to the server via HTTP, call a chatbot API (e.g., OpenAI), and return the response. This works for one-on-one chats with a bot.
  • Pros: Simple, no need for persistent connections.
  • Cons: Slower for group chats or frequent bot interactions due to HTTP overhead.

• WebSocket-Based Chatbot:

  • Use WebSockets to handle user and bot messages in real time, especially in group chats where the bot responds to multiple users instantly.
  • Pros: Feels seamless, supports complex scenarios.
  • Cons: Requires WebSocket setup, adding complexity.

Recommendation: For a single user chatting with a bot, HTTP is enough. For group chats or instant bot responses, use WebSockets. You can mix both: WebSockets for user-to-user messages and HTTP for bot API calls to keep things simple.

5. Managing Sessions and Preventing Data Loss: A Story-Based Journey

A robust chat app ensures users don’t lose messages or their place in the conversation, even if they refresh the page or the server crashes. Let’s explore this through three scenarios, introducing solutions like session management, local storage, message batching, and backup queues.

Scenario 1: Page Refresh Wipes Out Chats

Story: Alice is chatting with Bob about their weekend plans. She sends a message, sees it in the chat, and accidentally refreshes the page. Disaster—her chat history is gone! She’s annoyed, thinking the app is broken.

Solution: Session Management and Local StorageTo fix this, track users with a session ID and store messages locally in the browser using IndexedDB (for larger datasets) or localStorage (for simplicity).

• Session Management: Create a unique session ID when a user joins. Store it in localStorage and include it in every message to identify the user.

// components/Chat.js
  function getSessionId() {
    let sessionId = localStorage.getItem('sessionId');
    if (!sessionId) {
      sessionId = Math.random().toString(36).substring(2);
      localStorage.setItem('sessionId', sessionId);
    }
    return sessionId;
  }

  const sendMessage = () => {
    if (message.trim()) {
      const msg = { sessionId: getSessionId(), text: message };
      socket.emit('send_message', msg);
      setReceivedMessages((prev) => [...prev, msg]);
      setMessage('');
    }
  };

• Local Storage with IndexedDB: Cache messages in IndexedDB and load them on page refresh.

// components/Chat.js
  import { openDB } from 'idb';

  async function storeMessage(message) {
    const db = await openDB('chatDB', 1, {
      upgrade(db) {
        db.createObjectStore('messages', { autoIncrement: true });
      },
    });
    await db.add('messages', message);
    db.close();
  }

  async function getMessages() {
    const db = await openDB('chatDB', 1);
    const messages = await db.getAll('messages');
    db.close();
    return messages;
  }

  useEffect(() => {
    getMessages().then((msgs) => setReceivedMessages(msgs));
    socket = io('http://localhost:3000');
    socket.on('receive_message', (msg) => {
      setReceivedMessages((prev) => [...prev, msg]);
      storeMessage(msg);
    });
    return () => socket.disconnect();
  }, []);

Outcome: Alice refreshes the page, and her chat history reloads from IndexedDB. The session ID keeps her identity consistent, so the server knows it’s her.

Scenario 2: Slow Network Makes Chatting Painful

Story: Bob is on a shaky train Wi-Fi, sending messages to Alice. He types five messages quickly, but the app sends each one separately. The network lags, and messages take ages to appear, making the chat feel clunky.

Solution: Batching MessagesQueue messages locally and send them in batches to reduce network requests, keeping the UI snappy.

• Implementation: Store messages in an array and send them when the queue hits a limit or after a short delay.

// components/Chat.js
  let messageQueue = [];

  function queueMessage(message) {
    messageQueue.push(message);
    storeMessage(message); // Save to IndexedDB
    if (messageQueue.length >= 5) {
      sendBatch();
    }
  }

  function sendBatch() {
    if (messageQueue.length > 0) {
      socket.emit('send_batch', messageQueue);
      messageQueue = [];
    }
  }

  setInterval(sendBatch, 3000); // Send every 3 seconds

  const sendMessage = () => {
    if (message.trim()) {
      const msg = { sessionId: getSessionId(), text: message };
      setReceivedMessages((prev) => [...prev, msg]);
      queueMessage(msg);
      setMessage('');
    }
  };

• Server Handling: Process batched messages and broadcast them.

// pages/api/socket.js
  socket.on('send_batch', (messages) => {
    messages.forEach((msg) => io.emit('receive_message', msg));
  });

Outcome: Bob’s messages queue locally, and the UI updates instantly. Batches are sent efficiently, so the chat feels smooth even on bad Wi-Fi.

Scenario 3: Server Crash Loses Messages

Story: Alice and Bob are planning a party in the chat. Suddenly, your server crashes for 15 minutes. Messages sent during the outage vanish, and users flood your inbox with complaints about lost chats.

Solution: Backup Queues and Persistent StorageUse a message queue (e.g., Redis) and a database (e.g., MongoDB) to ensure messages are never lost. Queue messages locally during outages and sync them when the server is back.

• Local Queue for Offline Support: Save messages to IndexedDB when the server is down and sync on reconnect.

// components/Chat.js
  socket.on('disconnect', () => {
    console.log('Server offline, queuing locally...');
  });

  socket.on('connect', () => {
    console.log('Server online, syncing...');
    getMessages().then((msgs) => {
      if (msgs.length > 0) {
        socket.emit('send_batch', msgs);
        // Clear IndexedDB after sync
        openDB('chatDB', 1).then((db) => {
          db.clear('messages');
          db.close();
        });
      }
    });
  });

• Server-Side Message Queue: Queue messages in Redis before saving to the database.

// pages/api/queue.js F
  import Redis from 'ioredis';

  const redis = new Redis(process.env.REDIS_URL);

  export default async function handler(req, res) {
    await redis.lpush('message_queue', JSON.stringify(req.body));
    res.status(200).json({ success: true });
  }

• Background Worker: Process the queue and save to MongoDB.

// scripts/worker.js
  import Redis from 'ioredis';
  import { MongoClient } from 'mongodb';

  const redis = new Redis(process.env.REDIS_URL);
  const client = new MongoClient(process.env.MONGODB_URI);

  async function processQueue() {
    await client.connect();
    const db = client.db();
    while (true) {
      const message = await redis.rpop('message_queue');
      if (message) {
        await db.collection('messages').insertOne(JSON.parse(message));
      }
    }
  }

  processQueue();

• Database Schema: Store messages persistently in MongoDB.

// MongoDB schema
  {
    sessionId: String,
    text: String,
    timestamp: Date
  }

Outcome: When the server restarts, Alice and Bob’s messages sync from IndexedDB to Redis, then to MongoDB. No messages are lost, and users trust your app.

Additional Considerations

• Durable Queues: Use RabbitMQ instead of Redis for critical apps, as it saves messages to disk, preventing loss in a crash.
  • Trade-Off: RabbitMQ is more reliable but slower and trickier to set up.
• Database Choice: MongoDB is flexible for chat data, but PostgreSQL is better for complex queries (e.g., analytics).
  • Trade-Off: MongoDB is fast for writes; PostgreSQL excels at relationships.
• Deduplication: Add a unique message ID to prevent duplicates if a message is sent twice during a retry.
• Monitoring: Use Datadog or Prometheus to track queue size, server uptime, and message delivery times.

6. Conclusion: Your Path to a Robust Chat App

You’ve transformed a basic chat input form into a reliable, real-time chat application. WebSockets with Socket.IO brought instant messaging to life. Session management and IndexedDB ensured chats survive page refreshes. Batching messages kept the app fast on slow networks. Redis and MongoDB, paired with local queuing, made your app resilient to server outages. Whether you add a chatbot via HTTP or WebSockets, your app is now ready for real users.

Next Steps:

• Add typing indicators, read receipts, or group chats.
• Use load testing tools like Artillery to simulate many users.
• Consider end-to-end encryption for privacy.
• Ask users for feedback to guide new features.

Building a chat app teaches you real-time communication, state management, and scalability. Start small, keep iterating, and soon you’ll have an app users can’t stop using.

Resources:

• Socket.IO Documentation
• MongoDB for Real-Time Apps
• Redis Pub/Sub for Chat
• Building a Chat App with React and Node.js