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

Adding this because I've spent hours trying to figure it out...

If you configured your health check endpoint but it still says Out of Service, it might be because your server is redirecting the request (i.e. returning a 301 or 302 response).

For example, if your endpoint is supposed to be /app/health/ but you only enter /app/health (no trailing slash) into the health check endpoint field on your ELB, you will not get a 200 response, so the health check will fail.