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

I was working on the AWS Tutorial on hosting a web app and ran into this problem. Step 7b states the following:

"Set Ping Path to /. This sends queries to your default page, whether it is named index.html or something else."

They could have put the forward slash in quotations like this "/". Make sure you have that in your health checks and not this "/." .

Answer 2

If your web server is running fine, then it means the health check goes on a url that doesn't return 200.

A trick that works for me : go on the instance, type curl localhost:80/pathofyourhealthcheckurl

After you can adapt your health check url to always have a 200 response.

Answer 3

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.

Answer 4

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.

Answer 5

I contacted AWS support about this same issue. Apparently their system doesn't know how to handle cases were all of the instances behind the ELB are stopped for an extended amount of time. AWS support can manually refresh the statuses, if you need them up immediately.

The suggested fix it to de-register the ec2 instances from the ELB instead of just stopping them and re-register them when you start again.

Answer 6

I would like to provide you a general way to solve this problem. When you have set up you web server like apache or nginx, try to read the access log file to see what happened. In my occasion, it report 401 error because I have add the basic auth in nginx. Of course, just like @ivankoni remind, it may because of the document you check is not exist.