Real-Time Features: SSE, WebSockets, or Polling?

Real-time features — live notifications, chat, collaborative editing, live dashboards — are no longer nice-to-haves. Users expect instant updates. The question is which technology to use: Server-Sent Events (SSE), WebSockets, or plain polling.

Polling is the simplest approach. Your client sends a request to the server every N seconds asking "anything new?" It's easy to implement, works everywhere, and uses standard HTTP. The downside: it's wasteful. Most requests return nothing, burning bandwidth and server resources. Use polling only when updates are infrequent (every 30+ seconds) and simplicity outweighs efficiency.

Server-Sent Events (SSE) establish a one-way stream from server to client over a standard HTTP connection. The server pushes updates whenever they happen — no wasted requests. SSE handles reconnection automatically, works through most proxies and firewalls, and uses simple text-based messages. The limitation: it's one-directional. The client can't send data back through the same connection.

WebSockets create a full-duplex, bidirectional connection between client and server. Both sides can send messages at any time. This is ideal for chat applications, multiplayer games, or collaborative editors where both parties need to send data frequently. The cost: more complex server infrastructure, potential issues with load balancers and proxies, and manual reconnection logic.

For most business applications — notifications, activity feeds, live status updates, dashboard refreshes — SSE is the sweet spot. It's simpler than WebSockets, more efficient than polling, and handles 90% of real-time use cases. We use SSE in our own platform for project updates, message notifications, and payment status changes.

Scaling considerations: SSE and WebSockets both maintain persistent connections, which consumes server memory. A single Node.js server can handle 10,000-50,000 concurrent connections comfortably. Beyond that, you need Redis pub/sub or a similar message broker to coordinate across multiple server instances.

Choose polling for simplicity on non-critical features, SSE for server-to-client push (most cases), and WebSockets only when you need bidirectional real-time communication. Start with the simplest solution that meets your requirements — you can always upgrade later.