Two Approaches to Real-Time

Real-time features — live notifications, chat, dashboards, collaborative editing — require pushing data from server to client. WebSockets and Server-Sent Events (SSE) are the two primary protocols for this, each with distinct strengths. At Nexis Limited, we choose between them based on the specific requirements of each feature in our SaaS products.

Server-Sent Events (SSE)

SSE is a simple, HTTP-based protocol for one-directional communication from server to client. The client opens a standard HTTP connection, and the server sends events as they occur. The connection stays open indefinitely.

Strengths

  • Built on HTTP — works with existing infrastructure (load balancers, proxies, CDNs).
  • Automatic reconnection — the browser handles reconnection and event ID tracking natively.
  • Simple — no handshake protocol, no special server library needed. Any HTTP server can stream SSE.
  • Text-based — easy to debug with browser DevTools.

Limitations

  • One-directional — server to client only. Client sends data via standard HTTP requests.
  • Text only — binary data must be base64 encoded.
  • Connection limit — browsers limit concurrent SSE connections per domain (6 in HTTP/1.1, unlimited in HTTP/2).

WebSockets

WebSockets provide full-duplex, bidirectional communication over a single TCP connection. After an HTTP upgrade handshake, the connection switches to the WebSocket protocol for low-overhead message exchange.

Strengths

  • Bidirectional — both client and server can send messages at any time.
  • Low overhead — after the handshake, message frames have minimal headers (2-14 bytes).
  • Binary support — native support for binary data (images, files, protocol buffers).
  • Lower latency — no HTTP overhead per message.

Limitations

  • No automatic reconnection — you must implement reconnection logic.
  • Infrastructure complexity — requires WebSocket-aware load balancers and proxies.
  • Stateful connections — harder to scale horizontally than stateless HTTP.

When to Choose SSE

  • Live notifications — push alerts from server to client.
  • Real-time dashboards — stream metric updates to the browser.
  • News feeds and activity streams — push new items as they happen.
  • AI/LLM streaming — stream generated text token by token (ChatGPT-style).

When to Choose WebSockets

  • Chat applications — bidirectional message exchange.
  • Collaborative editing — real-time document synchronization.
  • Gaming — low-latency state synchronization.
  • Binary data streaming — audio, video, or file transfer.

Scaling Considerations

Both SSE and WebSockets maintain persistent connections, which consumes server resources. Scaling strategies include:

  • Use Redis Pub/Sub or Kafka to broadcast events across multiple server instances.
  • Implement connection limits and graceful degradation under high load.
  • Use a dedicated real-time service instead of running WebSockets on your API server.
  • Consider managed services like Pusher, Ably, or AWS AppSync for WebSocket infrastructure.

Conclusion

SSE is simpler and sufficient for most real-time use cases where communication flows from server to client. WebSockets are necessary when bidirectional communication or binary data is required. Default to SSE for simplicity and use WebSockets when the use case demands it.

Building real-time features? Our team implements real-time communication architecture.