Real-time Protocols — Notes

Heartbeat / keep-alive

• WS: send ping frame every 20-30 s; close conn if no pong in 2× interval.
• SSE: send : comment\n\n every 15 s.
• Long-poll: set server response timeout < intermediary idle timeout.

Backpressure

• WS / SSE have no built-in flow control — application must drop or coalesce on slow clients.
• gRPC streaming uses HTTP/2 flow control (per-stream + connection windows).

Auth at the edge

• Use cookies or Authorization header for HTTP-based (SSE).
• For WS, browsers can't set custom headers on the upgrade — pass auth as query param or sub-protocol, or do an HTTP login first that sets a cookie.

Capacity

• Plan ~10 KB RSS per idle WS connection.
• 200k conns × 10 KB = 2 GB per gateway box; tune fs.file-max, net.ipv4.tcp_*.

Refs

• RFC 6455 (WebSocket), WHATWG SSE spec.
• "Designing for Throughput" — Cloudflare Workers WS blog.
• Slack / Discord / Phoenix Channels architecture posts.