Specifically, I'm running a Flask app with default workers in gunicorn. I'm trying to figure out how to debug / trace what is happening when a worker is killed due to timeout while serving a request. Is there a way to get a stack trace or profile the request to debug this?
Just wanted to add to the accepted answer that there's, also, another way to get similar results by using the built-in Python 3 module faulthandler introduced in v3.3 https://docs.python.org/dev/library/faulthandler.html
You can add the following two lines to wsgi.py mentioned in the accepted answer:
import faulthandler
faulthandler.enable()
When timeout occurs the following output will be printed to stderr:
[2020-12-24 13:38:32 +0000] [31304] [INFO] Starting gunicorn 20.0.4
[2020-12-24 13:38:32 +0000] [31304] [INFO] Listening at: http://0.0.0.0:8888 (31304)
[2020-12-24 13:38:32 +0000] [31304] [INFO] Using worker: sync
[2020-12-24 13:38:32 +0000] [31307] [INFO] Booting worker with pid: 31307
[2020-12-24 13:38:55 +0000] [31304] [CRITICAL] WORKER TIMEOUT (pid:31307)
Fatal Python error: Aborted
Current thread 0x00007f411d781700 (most recent call first):
File "/tmp/app.py", line 14 in c
File "/tmp/app.py", line 9 in b
File "/tmp/app.py", line 6 in a
File "/tmp/app.py", line 20 in catch_all
File "/tmp/venv/lib/python3.5/site-packages/flask/app.py", line 1936 in dispatch_request
File "/tmp/venv/lib/python3.5/site-packages/flask/app.py", line 1950 in full_dispatch_request
File "/tmp/venv/lib/python3.5/site-packages/flask/app.py", line 2447 in wsgi_app
File "/tmp/venv/lib/python3.5/site-packages/flask/app.py", line 2464 in __call__
File "/tmp/venv/lib/python3.5/site-packages/gunicorn/workers/sync.py", line 175 in handle_request
File "/tmp/venv/lib/python3.5/site-packages/gunicorn/workers/sync.py", line 134 in handle
File "/tmp/venv/lib/python3.5/site-packages/gunicorn/workers/sync.py", line 29 in accept
File "/tmp/venv/lib/python3.5/site-packages/gunicorn/workers/sync.py", line 67 in run_for_one
File "/tmp/venv/lib/python3.5/site-packages/gunicorn/workers/sync.py", line 123 in run
File "/tmp/venv/lib/python3.5/site-packages/gunicorn/workers/base.py", line 140 in init_process
File "/tmp/venv/lib/python3.5/site-packages/gunicorn/arbiter.py", line 583 in spawn_worker
File "/tmp/venv/lib/python3.5/site-packages/gunicorn/arbiter.py", line 616 in spawn_workers
File "/tmp/venv/lib/python3.5/site-packages/gunicorn/arbiter.py", line 545 in manage_workers
File "/tmp/venv/lib/python3.5/site-packages/gunicorn/arbiter.py", line 202 in run
File "/tmp/venv/lib/python3.5/site-packages/gunicorn/app/base.py", line 72 in run
File "/tmp/venv/lib/python3.5/site-packages/gunicorn/app/base.py", line 228 in run
File "/tmp/venv/lib/python3.5/site-packages/gunicorn/app/wsgiapp.py", line 58 in run
File "/tmp/venv/bin/gunicorn", line 8 in <module>
[2020-12-24 13:38:55 +0000] [31307] [INFO] Worker exiting (pid: 31307)
[2020-12-24 13:38:55 +0000] [31503] [INFO] Booting worker with pid: 31503