Status Code 460 on Application Load Balancer

Question

I'm seeing a concerning amount of 460 status codes in the logs of my Application Load Balancer. I don't see any patterns on these codes in regards to times, servers, or request URLs. According to this forum post, the 460 means:

The client has closed the connection with the ALB before the idle timeout has kicked in on either the front-end or the back-end connection.

I can see the request making it to the backend server and the backend processes the request without issue and very quickly. Why are these errors happening? This ALB does a significant amount of traffic with 6-8 backend servers.

Example ALB Log:

https 2017-01-30T22:46:27.451363Z app/LOAD-BALANCER/bbab458ad0b80d X.X.X.X:55999 10.5.X.X:80 0.000 -1 -1 460 - 132 0 "GET https://www.website.com:443/app/page HTTP/1.1" "-" ECDHE-RSA-AES128-SHA TLSv1 arn:aws:elasticloadbalancing:us-west-2:743462462234:targetgroup/TARGET-GROUP/e6120e5adr245b79107e "Root=1-588fc23e-77aea5adf4534af3de09659d13a08"

Example NGINX log from the backend:

X.X.X.X 1485807955.048 www.website.com /app/page - GET 200 - 0.056 24 text/html; charset=UTF-8 -

Answer 1

The documentation for the status code 460 is updated for Application Load Balancers.

This error occurs when the load balancer received a request from a client, but the client closed the connection with the load balancer before the idle timeout period elapses.

Check whether the client timeout period is greater than the idle timeout period for the load balancer. Ensure that your target provides a response to the client before the client timeout period elapses, or increase the client timeout period to match the load balancer idle timeout, if the client supports this.

You can read the full doc here: http://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-troubleshooting.html#http-460-issues