WebSockets vs Server-Sent Events (SSE): Architecting Real-Time Apps

The Real-Time Dilemma

Building a chat application, live dashboard, or collaborative document editor requires real-time data sync. For years, the default answer was "just use WebSockets." However, as architectures move toward serverless and edge compute, maintaining persistent WebSocket connections has become an expensive infrastructure challenge.

WebSockets: Bidirectional Power

WebSockets provide a full-duplex, persistent connection over TCP. Both the client and server can push messages at any time with virtually zero overhead.

• Best for: Multiplayer games, collaborative editing (like Figma), and high-frequency trading dashboards.
• Drawback: They are stateful. Load balancing WebSocket servers requires complex sticky sessions and Redis pub/sub backplanes.

Server-Sent Events (SSE): The Lightweight Alternative

SSE operates over standard HTTP. It provides a unidirectional flow of data from the server to the client. The client opens a request, and the server keeps the stream open to push text data indefinitely.

• Best for: Live sports scores, AI streaming responses (like ChatGPT), and live social media feeds.
• Advantage: Because SSE uses standard HTTP, it automatically works with standard load balancers, HTTP/2 multiplexing, and corporate firewalls.

The Verdict

Do not default to WebSockets unless your client is pushing high-frequency data back to the server. For 80% of use cases (including notifications and live feeds), Server-Sent Events (SSE) offer a massively simpler and more scalable architecture.