flask application timeout with amazon load balancer

Question

I'm trying to use a Flask application behind an Amazon Load Balancer and the Flask threads keep timing out. It appears that the load balancer is sending a Connection: keep-alive header and this is causing the Flask process to never return (or takes a long time). With gunicorn in front the processes are killed and new ones started. We also tried using uWSGI and simply exposign the Flask app directly (no wrapper). All result in the Flask process just not responding.

I see nothing in the Flask docs which would make it ignore this header. I'm at a loss as to what else I can do with Flask to fix the problem.

Curl and direct connections to the machine work fine, only those via the load balancer are causing the problem. The load balancer itself doesn't appear to be doing anything wrong and we use it successfully with several other stacks.

Answer 1

The solution I have now is using gunicorn as a wrapper around the flask application. For the worker_class I am using eventlet with several workers. This combination seems stable and responsive. Gunicorn is also configured for HTTPS.

I assume it is a defect in Flask that causes the problem and this is an effective workaround.