Instructions

Choose and sketch real-time delivery in Next.js (App Router Route Handlers or a dedicated Node service). Read realtime-transports.md before picking SSE vs WebSocket.

When to Use

• Use when notifications, live logs, progress, chat, or collaborative edits need a push channel.
• Prefer polling / revalidate first if latency tolerance is seconds, not milliseconds.
• Prefer auth-handbook for session or short-lived ticket minting.
• Prefer api-handbook for upgrade failure error shapes.

1. SSE: one-way server → browser; good for notifications, live logs, progress. CORS if cross-origin; reconnection with Last-Event-ID when you implement resume.
2. WebSockets: full-duplex; chat, collaborative editing. Prefer a short-lived ticket minted server-side when cookie attachment on handshake is unreliable.
3. Where it runs: default Node for long-lived connections; Edge is often wrong for fan-out - justify runtime per deployment.
4. Scale: sticky sessions or shared pub/sub for multi-instance; document single-node limits.
5. Backpressure: slow clients must not block the server - bounded queues, drop or disconnect policy.
6. Abuse: rate-limit connects and messages on user-facing endpoints.

Outcomes