WebSockets vs HTTP Polling: When Real-Time Actually Needs WebSockets

HTTP is a request-response protocol — the client sends a request, the server sends a response, the connection closes. Every interaction requires a new connection or explicit keep-alive. WebSockets provide a persistent, bidirectional connection. After an initial HTTP upgrade handshake, the connection stays open and either side can send messages at any time with minimal overhead. HTTP is stateless and requires the client to initiate all communication. WebSockets maintain connection state and allow server-initiated messages. The overhead per message is dramatically lower for WebSockets (a few bytes) compared to HTTP (hundreds of bytes of headers per request).

Server-Sent Events (SSE) is a simpler alternative to WebSockets for server-to-client one-way streaming. Using regular HTTP connections with a special Content-Type (text/event-stream), the server holds the connection open and pushes events as they occur. SSE is simpler to implement than WebSockets, works with standard HTTP infrastructure (proxies, CDNs, load balancers), and automatically reconnects. The limitation: it's unidirectional — only server to client. Client can't send messages through the same connection. SSE is the right choice when you need real-time data from server to client but don't need client-to-server messaging (live notifications, real-time dashboards, live feed updates).

Regular polling: client sends a request every N seconds, server responds immediately (with data or 'nothing new'). Long polling: client sends a request, server holds the connection open until it has something to send or a timeout occurs. When the server responds, the client immediately sends another request. Long polling simulates server push with HTTP — the client is always waiting for the next response. The advantage over regular polling is lower latency (response arrives immediately when data is available) and fewer requests when data arrives infrequently. The disadvantage is connection overhead and complexity. SSE is generally preferred over long polling for new implementations.