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Server-Sent Events (SSE) stream text from a server to a client over a standard HTTP response. Applications use them for live dashboards, progress updates, notifications, and AI token streams. Bunny CDN supports SSE, and there is no setting to enable. An event stream is an ordinary HTTP response with the text/event-stream content type, and the edge delivers each event as soon as your origin writes it. SSE works with every origin type:

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Keep the stream out of the cache

Send Cache-Control: no-cache from your origin. An event stream is cached like any other response. An origin that sends no Cache-Control gets the pull zone’s default cache time of 1 month.
A cached stream is no longer a stream. Later clients receive a recording of the first client’s events, all at once, followed by the end of the response. The browser then reconnects, receives the same recording, and loops. Two settings cache a stream even when your origin asks for no caching:
  • An Override Cache Time Edge Rule that matches the path of the stream.
  • Ignore Query Strings on the pull zone. The cache key is then the path alone, so a per-user stream selected by a query parameter is served to every user.
Request Coalescing joins simultaneous requests for the same URL into one origin request. This is correct for a shared feed, but not for a per-user stream. Give each client its own URL when you use it.

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Keep the stream active

The edge closes a connection that carries no data for approximately two minutes. This is the only duration limit on an event stream, and the connection stays open as long as data flows. Send a heartbeat at least every 30 seconds when you have no events to deliver. An SSE comment line is sufficient, because the client ignores it and the bytes reset the timer:
There is no guaranteed maximum duration. An edge server can close a stream at any time, for example during maintenance. The client sees a connection error and not a clean end of the response, so always let the client reconnect.
Give each event an id field. The client sends the last identifier back in the Last-Event-ID header when it reconnects, which lets your origin continue from that point.

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Origin requirements

  • Send the first event immediately. Nothing reaches the client before the first byte, and until it arrives a healthy stream looks the same as a failed connection. An event that carries the current state works well as the first event, and a comment line is sufficient when you have no state to send.
  • Send the response headers immediately. Bunny waits 60 seconds for your origin to start the response, and returns a 504 Gateway Timeout with error code 106 if nothing arrives. The limit applies only until the headers arrive, and not to the stream that follows. See 502 and 504 errors.
  • Flush each event. Output buffering in your framework or your web server holds events back, and the client receives them late or in one block.
  • Remove any request time limit on the origin route that serves the stream.

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Pricing

An event stream is a standard HTTP request, and Bunny bills the data it transfers at the normal CDN bandwidth rate. The WebSocket connection limits and the WebSocket connection-time price do not apply. An Edge Script that produces the stream also bills CPU time and requests, and not the time the connection stays open.

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SSE or WebSockets

Last modified on August 31, 2026