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Keep a long, quiet request alive - #330
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Calls to the render service carry nothing on the connection for minutes at a time while the service works on the answer. Network equipment between the two drops a connection that quiet and tells neither end, so the answer has nowhere to go. The client then waits for an answer that cannot arrive, with no read timeout to end the wait and nothing on the connection to tell it the other end is gone. Every request now goes through a session whose connections carry keepalive. The probes put a packet on the connection often enough to keep it, and they end the connection when the other end has really gone, which the retry logic already treats as a network error. A render of the dashboard waited one hour and fifty-six minutes this way. The service had answered it with 200 after six and a half minutes.
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Check name Status Explanation Description Check Check skipped - CodeRabbit’s high-level summary is enabled. Title check The title clearly and concisely describes the main change: keeping long-running, idle API requests alive through TCP keepalive probes. Linked Issues check Check skipped because no linked issues were found for this pull request. Out of Scope Changes check Check skipped because no linked issues were found for this pull request.
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Review comments at @codeplain_REST_api.py:
- Around line 52-54: Update KeepaliveAdapter to configure proxy connections as
well as direct connections by overriding proxy_manager_for and passing
keepalive_socket_options() through its proxy manager arguments. Preserve the
existing init_poolmanager behavior.
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Maybe worth considering adding retries to the mentioned calls below. Other than that looks like great change & fix!
Hidden behaviour change: connections are now reused. Before, each requests.post used a fresh session and a fresh connection. Now connections are pooled and reused between calls, and there can be minutes of local test runs between calls. If the server or load balancer closes an idle pooled connection just as the client reuses it, the call fails with a ConnectionError.
- Render calls retry, so they're fine.
connection_check,statusandrender_finishedusenum_retries=0, so they fail outright.render_finishedis the most exposed: it runs after the longest idle gap, and its failure is swallowed silently.- Fix: let those calls retry once on
ConnectionError, or use a fresh session for them.
A request that goes through a proxy is served from a separate pool, which the keepalive options never reached. A render behind a proxy is as quiet as any other, so it was still open to the connection being dropped. The pool a proxy uses now gets the same options as a direct one.
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Implemented in f4662bd. Checked that it reaches the proxy pool rather than assuming it: a |
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The client no longer waits forever for an answer that cannot arrive.
What happens now
A call to the codeplain API can sit with nothing on the connection for several minutes while the service works. This is expected because the underlying LLM calls can take a while. The client now sends keepalive probes during that wait, so the connection stays open and the answer gets back.
Why it was needed - why the connection doesn't stay open
In some cases, renders run on GitHub hosted runners, which sit on Azure. Their outbound traffic passes through network address translation, and Azure drops a translated connection that has carried nothing for four minutes. Neither end is told. The client has no read timeout (presumably because we anticipate long LLM calls), so it waits for as long as the GitHub runner allows.
One render waited 1 hour 56 minutes for an answer the codeplain API had already sent after 6 minutes 37 seconds (but ~4 minutes in, the TCP channel was dropped).
The service was not stuck during that silence, and the logs say so plainly. It spent the time asking the model for a fix to a failing test, and wrote a line for each step as it went. It then recorded the call as finished, successful, and 6 minutes 37 seconds long. Nothing on the service side looks wrong. Only the client never saw the answer.
How I verified this
I created a new endpoint on the codeplain API that waits a chosen number of seconds and then answers, sending nothing meanwhile. A script in a job on a GitHub runner called it over a range of waits, with keepalive and without. Answers that came back:
Without keepalive the connection is cut after 261 seconds, nine times out of nine. With keepalive nothing was cut.
In the measurement the client was told the connection had gone. The render that hung was never told. Keepalive stops the cut either way.
What this looks like in the logs
This is a recent job that stalled after 39 minutes but I left the job running past 2 hours:
https://github.com/Codeplain-ai/codeplain-dashboard/actions/runs/37907583732/job/115272675363
And the langsmith traces show that between 12:08:20 and 12:13:29 there were a few calls between the codeplain-api and the LLM (list_files_applicable_for_conformance_test_generation -> fix_conformance_tests_issue -> review_conformance_tests_fix -> fix_conformance_tests_issue -> review_conformance_tests_fix) and that took 309s. In that time, the connection was dropped and the client was left hanging.
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