Server-Sent Events: Simpler Real-Time Alternative to WebSockets

Server-Sent Events (SSE) offer a simpler alternative to WebSockets when you only need one-way communication from server to client. Unlike WebSockets' bidirectional connection, SSE establishes a persistent HTTP connection where the server pushes data to the client. The EventSource API is native to browsers and significantly easier to implement than WebSocket protocols. Use cases include live dashboards, real-time notifications, news feeds, stock tickers, and progress updates for long-running tasks. On the server, you set the Content-Type to text/event-stream and keep the connection open, sending data with the format "data: {json}\n\n". Reconnection is automatic—if the connection drops, EventSource attempts to reconnect with exponential backoff. You can include custom event types and message IDs for reliable delivery. SSE uses standard HTTP, works through most proxies, and supports HTTP/2 for efficient multiplexing. The main limitation is browser connection limits (typically 6 concurrent connections), so it's not suitable for apps requiring thousands of simultaneous connections. Implementation patterns include using Redis pub/sub to broadcast events to multiple server instances, and using compression for bandwidth efficiency. For frameworks, Express supports SSE with simple response object manipulation, while libraries like RxJS provide reactive wrappers. Compared to WebSockets, SSE reduces complexity significantly when the communication pattern is server-to-client only. For many real-time features, SSE is the simpler, more appropriate choice.