SSE appears to sometimes not be flushing all the way to the client – is it proxy related?

  html, javascript, proxy, server-sent-events

I’m using SSE (Server Sent Events) to send notifications to the browser. Most of the time the implementation works fine but in some cases I can see that no events are reaching the client.

Looking at the telemetry and logs my best guess is that some proxy along the request is buffering the response waiting for it to complete before sending it to the end client. I’ve observed the same client receive the events when the response completes. I don’t believe this is an issue on the server side or I’d have been able to observe it, which is why I’m guessing it’s a proxy outside of my control.

Is this a common problem with SSE? If so, is there any way to solve it? Any header to hint to the proxy that this can be flushed immediately?

Source: Ask Javascript Questions