Q:

Why can't I access Flask API through load balancer on AWS

I deployed a Flask app with Gunicorn on EC2 instance via port 8080.  Now I want to set up a load balancer to enable SSL and link to a domain eventually.  The swagger page can be accessed by http://ec2-dns:8080/api.  A classic type of load balancer is created with the EC2 added.  Health Check is good.  But when I tried to hit the endpoints using the load balancer's dns name https://lb-dns/api, it would time out with 408. 
Why is it not working with the load balancer? 

A:

you listener should be looked like this 

also check the security group has the right port opening

