Why does Elastic Load Balancing report 'Out of Service'?

Question

I am trying to set up Elastic Load Balancing (ELB) in AWS to split the requests between multiple instances. I have created several images of my webserver based on the same AMI,

Answer 1

For anyone else that sees this thread as this isn't listed:

Check that the health check is checking the port that the responding server is listening on.

E.g. node.js running on port 3000 -> Point healthcheck to port 3000;

Not port 80 or 443. Those are what your ALB will be using.

I spent a morning on this. Yes.