How do you handle real-time features like live updates or chat?

Real-time features push data to clients immediately rather than requiring them to poll. Several technologies enable this.

WebSockets provide full-duplex communication. Once connected, both client and server can send messages anytime. Ideal for chat, collaborative editing, or any bidirectional communication. Libraries like Socket.io add fallbacks, rooms, and broadcasting on top of raw WebSockets.

Server-Sent Events (SSE) are simpler for one-way updates (server to client). They work over regular HTTP, auto-reconnect on failure, and are supported natively in browsers with EventSource. Perfect for notifications, live feeds, or dashboards where clients only receive data.

Implementation considerations: WebSockets require sticky sessions or shared state (Redis pub/sub) when load balancing across multiple servers. Every connected client maintains a connection, which has resource implications at scale.

Managed services (Pusher, Ably, Supabase Realtime) handle the infrastructure complexity. They provide pub/sub channels, presence indicators, and scale automatically. Good when you want real-time without managing WebSocket servers.

For presence (who's online, who's typing), maintain heartbeats from clients and track state server-side. Presence information is typically ephemeral—stored in Redis or the real-time service rather than your primary database.

Choose SSE for simple broadcasts, WebSockets for bidirectional needs, and managed services when you want simplicity or expect significant scale.