From 721b955c2e5d286db0c2bd7e417fbfbccd191135 Mon Sep 17 00:00:00 2001
From: AndreKanmegne <andrelaurelyvan.kanmegnetabouguie@ynov.com>
Date: Mon, 15 Jun 2026 09:32:15 +0200
Subject: [PATCH] fix(rag): add sse keepalive heartbeat to prevent nginx 60s
 timeout (#434)
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the embedding phase (multi-query expansion via cpu-only ollama) can take
several minutes. nginx's proxy_read_timeout (60s default) was killing the
idle sse connection before any event was flushed, leaving the ui stuck on
"retrieving context…" forever.

send a sse comment (: keepalive) every 20s to keep the connection alive
through the entire pipeline duration.
---
 backend/controllers/ragController.js | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/backend/controllers/ragController.js b/backend/controllers/ragController.js
index 81d3503..5983e70 100644
--- a/backend/controllers/ragController.js
+++ b/backend/controllers/ragController.js
@@ -84,6 +84,13 @@ export const askQuestionStream = catchAsync(async (req, res) => {
     closed = true;
   });
 
+  // Keep the SSE connection alive through nginx's proxy_read_timeout (default 60s).
+  // The embedding phase can take minutes on CPU-only ollama — without this, nginx
+  // kills the idle connection before the first event is ever flushed.
+  const heartbeat = setInterval(() => {
+    if (!closed && !res.writableEnded) res.write(': keepalive\n\n');
+  }, 20000);
+
   try {
     await executeRAG({
       question,
@@ -104,6 +111,7 @@ export const askQuestionStream = catchAsync(async (req, res) => {
       send('error', { message: 'Stream failed', code: 'STREAM_ERROR' });
     }
   } finally {
+    clearInterval(heartbeat);
     if (!res.writableEnded) res.end();
   }
 });