Our app's REST API is served by Gunicorn (not behind Nginx) running on AWS EC2 instances with a typical auto-scaling/load balancing setup. The load balancer's idle timeout is 60 seconds, and Gunicorn's keep-alive timeout is 2 seconds. We've been seeing sporadic
504 Gateway Timeout responses from this configuration. According to Amazon docs, this may be because the server's keep-alive timeout is lower than the load balancer's idle timeout setting:
Cause 2: Registered instances closing the connection to Elastic Load Balancing.
Solution 2: Enable keep-alive settings on your EC2 instances and set the keep-alive timeout to greater than or equal to the idle timeout settings of your load balancer.
With Nginx, the default
keepalive_timeout is 75 seconds, which apparently works well with the ELB default settings. However, Gunicorn docs recommend a
keepalive setting in the range of 1-5 seconds.
Does it make sense to bump Gunicorn's keepalive to 75 seconds, or is there a good reason for keep it below 5 seconds even though we're not using a reverse proxy in front of it?