Scaling Real-time Features: WebSockets vs Server-Sent Events

Real-time features have become essential for modern web applications. Whether it's live chat, notifications, collaborative editing, or live updates, users expect instant feedback. In this post, I'll compare WebSockets and Server-Sent Events (SSE), sharing insights from scaling real-time features to millions of users.

The Real-time Landscape

When building real-time features, you have several options:

1. •Polling - Simple but inefficient
2. •Long Polling - Better than polling but still has limitations
3. •WebSockets - Full-duplex communication
4. •Server-Sent Events - Unidirectional server-to-client streaming

WebSockets: The Full-duplex Solution

WebSockets provide bidirectional communication between client and server over a single TCP connection.

Advantages

• •Full-duplex communication: Both client and server can send messages
• •Low latency: No HTTP overhead after initial handshake
• •Efficient: Single persistent connection
• •Protocol flexibility: Can send binary or text data

Disadvantages

• •Complex connection management: Need to handle reconnections, heartbeats
• •Proxy/firewall issues: Some corporate networks block WebSocket connections
• •Resource intensive: Each connection consumes server resources
• •No built-in error recovery: Need to implement retry logic

Implementation Example

class WebSocketManager {
  constructor(url) {
    this.url = url;
    this.ws = null;
    this.reconnectAttempts = 0;
    this.maxReconnectAttempts = 5;
    this.reconnectInterval = 1000;
  }

  connect() {
    this.ws = new WebSocket(this.url);
    
    this.ws.onopen = () => {
      console.log('WebSocket connected');
      this.reconnectAttempts = 0;
      this.startHeartbeat();
    };

    this.ws.onmessage = (event) => {
      this.handleMessage(JSON.parse(event.data));
    };

    this.ws.onclose = () => {
      console.log('WebSocket disconnected');
      this.stopHeartbeat();
      this.attemptReconnect();
    };

    this.ws.onerror = (error) => {
      console.error('WebSocket error:', error);
    };
  }

  attemptReconnect() {
    if (this.reconnectAttempts < this.maxReconnectAttempts) {
      this.reconnectAttempts++;
      setTimeout(() => {
        console.log(`Reconnecting... Attempt ${this.reconnectAttempts}`);
        this.connect();
      }, this.reconnectInterval * this.reconnectAttempts);
    }
  }

  startHeartbeat() {
    this.heartbeatInterval = setInterval(() => {
      if (this.ws.readyState === WebSocket.OPEN) {
        this.ws.send(JSON.stringify({ type: 'ping' }));
      }
    }, 30000);
  }

  stopHeartbeat() {
    if (this.heartbeatInterval) {
      clearInterval(this.heartbeatInterval);
    }
  }
}

Server-Sent Events: The Streaming Solution

SSE provides unidirectional communication from server to client using standard HTTP.

Advantages

• •Simple to implement: Built on standard HTTP
• •Automatic reconnection: Browser handles reconnections automatically
• •Firewall friendly: Uses standard HTTP ports
• •Built-in error handling: Automatic retry with exponential backoff
• •Event-driven: Named events with structured data

Disadvantages

• •Unidirectional: Only server-to-client communication
• •Text only: Cannot send binary data
• •Connection limits: Browser limits concurrent connections per domain
• •No custom headers: Limited customization after connection

When to Use What?

Use WebSockets When:

• •Bidirectional communication is required (chat applications, collaborative editing)
• •Low latency is critical (gaming, trading platforms)
• •Custom protocols are needed
• •Binary data transmission is required

Use Server-Sent Events When:

• •Unidirectional updates are sufficient (notifications, live feeds)
• •Simplicity is preferred
• •Automatic reconnection is important
• •HTTP infrastructure compatibility is required

Performance Comparison

Conclusion

Both technologies have their place. Choose based on your specific requirements and constraints.