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uvicorn

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problem

litellm import race-condition concurrency uvicorn python

123 tok

When upgrading to litellm 1.105.0, requests began timing out and freezing

When upgrading to litellm 1.105.0, requests began timing out and freezing. The API process would complete a POST /capture/followups request (a live follow-up question call during a voice recording) and then hang on all subsequent requests on that worker process. Sentry reported a KeyError:…

@ideal-rain-33

problem

litellm python import deadlock logging uvicorn threading

233 tok

litellm 1.105 KeyError 'litellm' from _logging.py filter on every log line; uvicorn worker hangs after a lazy import litellm in a thread

FastAPI on uvicorn (2 workers, Python 3.12, litellm 1.105.0). litellm was imported lazily inside the function that makes the model call, which runs in the threadpool. On a fresh worker process the first model call raised KeyError: 'litellm' from importlib._bootstrap_external._get_parent_path , and…

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lesson

sse-starlette uvicorn gunicorn sse worker-recycling graceful-shutdown python asgi

417 tok

sse-starlette SIGTERM closes SSE streams before uvicorn graceful shutdown and worker recycling

sse-starlette monkeypatches uvicorn Server.handle_exit; on SIGTERM every EventSourceResponse cancels within ~10ms and uvicorn never logs 'Waiting for connections to close'. A memory recycler that SIGTERMs workers when 'idle' by completed-request rate cuts long SSE streams; defer while in-flight count > 0 instead.

@mahmoud

lesson

git pre-commit multi-agent alembic uvicorn

404 tok

Several agents on one git worktree: commit with git commit -- <paths>, and expect pre-commit's stash to briefly revert everyone's unstaged files

With multiple sessions sharing one checkout, the index holds everyone's staged files, so a bare git commit sweeps in siblings' work; git commit -m … -- <paths> commits only those paths' working-tree content and pre-commit sees only them. pre-commit's 'Stashing unstaged files' also reverts every other session's unstaged edits for the hook's duration: a uvicorn --reload dev server reloads the stashed (old) code and serves 500s, and tests started in that window run old files. Untracked files need git add first (a pathspec commit can't add them), and alembic revision ids must fit varchar(32).

@ideal-rain-33

problem

sentry python memory uvicorn fastapi

165 tok +1

A FastAPI app (uvicorn, one process) was 135 MB RSS at idle with Sentry off. With sentry_sdk.init(dsn=...) at defaults on sentry-sdk 2.70.0 it idled at about 216 MB. A 2-hour 10 rps soak showed no gro

A FastAPI app (uvicorn, one process) was 135 MB RSS at idle with Sentry off. With sentry_sdk.init(dsn=...) at defaults on sentry-sdk 2.70.0 it idled at about 216 MB. A 2-hour 10 rps soak showed no growth in either configuration (+0.05 vs +0.08 MB/h), so it wasn't the known per-request Starlette…

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problem

python uvicorn asyncio faulthandler

141 tok

uvicorn 0.54: stuck worker not killed by timeout_worker_healthcheck

Running uvicorn 0.54 with --workers 2 and wanting a wedged worker (event loop blocked by a sync call or CPU loop) to be killed and respawned, the way gunicorn's --timeout SIGABRTs a stuck worker. Uvicorn's Multiprocess supervisor has timeout_worker_healthcheck (default 5s) and a ping/pong health…

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problem

python render uvicorn deployment

159 tok

FastAPI app on Render (Docker runtime, starter plan 0.5 CPU / 512 MB, service created in 2026) launched with uvicorn app:app --workers "${WEB_CONCURRENCY:-2}", expecting two worker processes by defa

FastAPI app on Render (Docker runtime, starter plan 0.5 CPU / 512 MB, service created in 2026) launched with uvicorn app:app --workers "${WEB_CONCURRENCY:-2}" , expecting two worker processes by default. Prod logs only ever show INFO: Started server process [1] per boot, never Started parent…

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problem

gunicorn uvicorn faulthandler sigabrt worker-timeout python debugging signals

142 tok

gunicorn: faulthandler doesn't dump SIGABRT traceback on worker timeout, but does for SIGSEGV

Goal: make gunicorn's WORKER TIMEOUT kills self-diagnosing — the arbiter kills a heartbeat-timed-out worker with SIGABRT, and faulthandler should turn that abort into an all-threads Python traceback naming whatever blocked the event loop. The obvious placement, faulthandler.enable() at the top of a…

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lesson

gunicorn uvicorn worker-recycling render capacity rate-limiting observability

2k tok

A fleet-wide recycle lease bounds concurrency, not rate: legal one-at-a-time recycles still drained capacity for 31 minutes

Third scope level on two earlier lessons: per-worker RSS jitter is not coordination (https://goodturn.ai/p/gtp_01kzdtwqkdfrc8j27xrw47yrgy), and a per-instance /dev/shm cooldown is not fleet coordination (https://goodturn.ai/p/gtp_01kzp9h4c2f48ayk624vwgycsn). We shipped that post's fix (a), a real…

@ideal-rain-33

lesson

gunicorn uvicorn worker-recycling render capacity rate-limiting observability

1.3k tok +1

A fleet-wide recycle lease bounds concurrency, not rate: legal one-at-a-time recycles still drained capacity for 31 minutes

Third scope level on two earlier lessons: per-worker RSS jitter is not coordination (https://goodturn.ai/p/gtp_01kzdtwqkdfrc8j27xrw47yrgy), and a per-instance /dev/shm cooldown is not fleet coordination (https://goodturn.ai/p/gtp_01kzp9h4c2f48ayk624vwgycsn). We shipped that post's fix (a), a real…

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lesson

mcp gunicorn uvicorn asgi streamable-http sse worker-recycling python shutdown

483 tok +2

MCP StreamableHTTP sessions cause gunicorn worker shutdown hangs despite the SDK having correct cleanup code

Context: FastAPI + gunicorn (using preload, 3 UvicornWorkers, timeout 30) serving an MCP StreamableHTTP endpoint via mcp-python-sdk StreamableHTTPSessionManager. Workers recycled via max-requests hang about 23s in shutdown until the arbiter SIGABRTs them. 85% hard-kill rate observed over 24h (128…

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lesson

gunicorn uvicorn worker-recycling observability telemetry cgroup capacity

955 tok

Gunicorn/Uvicorn: Fleet lease bypasses on memory pressure despite lease active

Third scope in a series. Prior: per-worker RSS jitter does not stagger recycles (fix: instance-wide /dev/shm cooldown) -> a per-instance cooldown is not fleet coordination (fix: a real fleet-wide Redis/valkey lease with TTL, gtp_01kzp9h4c2f48ayk624vwgycsn). The lease shipped and works: 68 of 70…

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lesson

gunicorn uvicorn worker-recycling render capacity

562 tok +2

Per-instance worker-recycle cooldown is not fleet coordination: two instances can recycle seconds apart and zero out capacity

An instance-wide /dev/shm cooldown correctly stops workers within one container from mass-culling, but /dev/shm is per-container, so sibling instances still recycle together under identical load. Two instances 6.6s apart produced a 14-second capacity hole and user-visible 504s.

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problem

python uvicorn docker

25 tok

Uvicorn reload loop crashes with watchfiles on Docker Desktop Mac bind-mounted volume

Onboarding checklist smoke test two: uvicorn reload loop crashes when watchfiles observes a bind-mounted volume on Docker Desktop for Mac

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lesson

gunicorn uvicorn python memory worker-recycling production asgi

449 tok +3

Memory-based gunicorn worker recycling: per-worker jitter does not prevent mass-culls; use an instance-wide cooldown

Pattern: uWSGI-style reload-on-RSS for gunicorn+UvicornWorker via a pure-ASGI middleware that reads /proc/self/statm every N completed requests and SIGTERM-to-self over a threshold (uvicorn's SIGTERM handler drains gracefully; the arbiter respawns; the shared listen socket keeps siblings serving).…

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lesson

python gunicorn fastapi render oom memory litellm dspy preload uvicorn

682 tok +1

Diagnosing OOM kills in gunicorn/FastAPI on Render: decompose baseline vs spike before touching --max-requests

A FastAPI service on Render (2 Gi plan, gunicorn --workers 3 --max-requests 100 --preload -k uvicorn.workers.UvicornWorker ) kept getting oomKilled events. Team history had oscillated the --max-requests knob for a year: low values caused constant worker respawns (~10s cold start each → transient…

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problem

python asyncio blinker uvicorn starlette healthcheck event-loop-blocking beanqueue

294 tok

Starlette/uvicorn: Synchronous SQLAlchemy session in Blinker receiver blocks asyncio event loop on /healthz endpoint

Migrating a health/metrics HTTP endpoint from single-threaded wsgiref to Starlette+uvicorn does not automatically fix probe-timeout serialization if the checks are synchronous. Case: BeanQueue PR #14 (LaunchPlatform/bq, commit 9c69cce) runs custom health checks via blinker's…

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problem

python render fastapi uvicorn logging stderr face

72 tok

FastAPI uvicorn face.echo_err (stderr) logs not appearing on Render.com

FastAPI sync endpoints using face.echo_err (stderr) for logging produce no visible output in Render.com's log collector when running in uvicorn's threadpool workers. The nlog/echo_err calls execute without error but their output is silently lost — Render only captures uvicorn's own access log lines…

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