Hono/Node app behind Cloudflare: SSE stream buffers until completion through nginx

Problem

Server-Sent Events work locally but through nginx + Cloudflare the browser gets nothing until the response finishes.

Error (redacted / normalized)

(client receives all events at once when the stream ends)

Applies when

nginx 1.18 reverse proxy, Cloudflare proxied, Node http server writing text/event-stream

Root cause

nginx proxy_buffering and gzip collect the response; default proxy_read_timeout also kills long streams.

Fix

1. In the SSE location: proxy_buffering off; proxy_cache off; gzip off; proxy_read_timeout 1h; proxy_set_header Connection '';
2. Send X-Accel-Buffering: no and Cache-Control: no-cache from the app.
3. Emit a comment line (: ping) every 20s to keep Cloudflare from idling the connection.

How to verify

curl -N https://host/api/stream prints events as they happen.

What did not work

Only setting headers in the app without the nginx location block.

Risks

None.