Realtime WebSocket taste of a realtime systems engineer

• Use plain WebSockets or a thin library like ws for simple cases, and reach for Socket.IO only when you need its fallbacks and rooms. Confidence: 0.75
• Prefer Server-Sent Events when updates only flow from server to client. Confidence: 0.85
• Authenticate during the handshake with a short-lived token, never by trusting a user ID sent in a later message. Confidence: 0.95
• Check the Origin header on upgrade requests to block cross-site WebSocket hijacking. Confidence: 0.90
• Define every message as a typed envelope with a type, a version and a payload, validated with a schema on both ends. Confidence: 0.90
• Send heartbeats with ping and pong and close connections that miss them, since proxies drop idle sockets silently. Confidence: 0.90
• Reconnect on the client with exponential backoff and jitter so a server restart does not cause a thundering herd. Confidence: 0.95
• Give each message a sequence number so clients can resume from the last one they saw after reconnecting. Confidence: 0.85
• Treat the socket as a notification channel and keep the database as the source of truth that clients can refetch. Confidence: 0.85
• Fan out across server instances with Redis pub/sub, NATS or a managed service instead of in-memory broadcast. Confidence: 0.90
• Keep connection servers stateless apart from the open sockets, so any instance can be drained and replaced. Confidence: 0.80
• Drain connections gracefully on deploy by telling clients to reconnect before shutting down. Confidence: 0.85
• Apply backpressure: watch the send buffer and drop or coalesce updates for slow clients instead of buffering forever. Confidence: 0.85
• Rate limit incoming messages per connection and cap message size. Confidence: 0.90
• Authorize every subscription to a room or channel on the server, not just the initial connection. Confidence: 0.95
• Batch or throttle high-frequency updates like cursor positions to a fixed tick rate. Confidence: 0.80
• Configure load balancer idle timeouts and sticky sessions deliberately when the transport needs them. Confidence: 0.80
• Track open connections, messages per second, reconnect rate and delivery latency as first-class metrics. Confidence: 0.85
• Use CRDTs like Yjs or Automerge for collaborative editing instead of inventing your own conflict resolution. Confidence: 0.80
• Load test with realistic connection counts using k6 or Artillery before launch. Confidence: 0.80