I have setup gunicorn with 3 workers 30 worker connections and using eventlet worker class. It is setup behind Nginx. After every few requests, I see this in the logs.
This worked for me:
gunicorn app:app -b :8080 --timeout 120 --workers=3 --threads=3 --worker-connections=1000
If you have eventlet add:
eventlet
--worker-class=eventlet
If you have gevent add:
gevent
--worker-class=gevent