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HTTP vs WebSockets vs Server-Sent Events
A protocol-level comparison of Short/Long Polling, Server-Sent Events (SSE), and WebSockets — evaluating connection lifecycles, framing overhead, horizontal scaling, and load-balancer state management.
WebSockets operate as a persistent, full-duplex TCP stream bypassing HTTP semantics after the handshake. Because WebSocket connections are stateful, standard stateless HTTP load balancers cannot distribute individual messages across backend pods.
Use Server-Sent Events (SSE) for unidirectional server-to-client streaming (e.g. LLM token streaming, real-time stock tickers, sports scores). Only use WebSockets when low-latency bidirectional client-to-server interaction is strictly required (e.g. collaborative canvases, multiplayer gaming).
- Compare Polling, Server-Sent Events (SSE), and WebSockets across latency, framing, and throughput
- Understand why SSE over HTTP/2 provides superior ergonomics for server-to-client streaming (AI responses, notifications)
- Analyze the operational complexity of scaling WebSockets across distributed server clusters using Redis Pub/Sub
- Make justified protocol decisions in system design interview scenarios
1. The Evolution of Real-Time Communication
Free Chapter PreviewHistorically, web clients received updates through inefficient workarounds:
- Short Polling: Client sends
GET /notificationsevery 2 seconds. 98% of responses are empty200 OK [], wasting mobile battery and server CPU on continuous TCP/TLS handshakes. - Long Polling: Server holds the HTTP connection open until data is ready. Better, but still incurs full HTTP header re-transmission on every single update.
Modern backends use native streaming protocols: Server-Sent Events (SSE) and WebSockets.
2. Server-Sent Events (SSE): Unidirectional Simplicity
In this section, we examine the production failure mechanics, internal socket buffers, and kernel-level trace diagnostics...
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