How to debug failed AWS elastic load balancer health checks

7
votes

I am at a loss trying to debug my ELB setup.

I have setup a load balancer with a single instance. I verified the configured health check works from the instance, and from another instance inside EC2. At this point I removed all possibly conflicting security group rules. Still the load balancer thinks the instance is not reachable.

I have copiously googled and gone through this checklist.

How can I get more information about the healthcheck failure? What is the closest thing I can do to sshing into the load balancer and reproducing the failure?

Thanks!

1
amazon-web-servicesamazon-ec2load-balancingamazon-elb

1 Answers

-3
votes

Your registered instances can fail the health check performed by your load balancer for one or more of the following reasons:

  • Problem: Instance(s) closing the connection to the load balancer.

    Cause: Elastic Load Balancing terminates a connection if it is idle for more than 60 seconds. The idle connection is established when there is no read or write event taking place on both the sides of the load balancer (client to load balancer and load balancer to the back-end instance).

    Solution: Set the idle timeout to at least 60 seconds on your registered instances.

  • Problem: Responses timing out.

    Cause: When the load balancer performs a health check, the instance may be under significant load and may take longer than your configured timeout interval to respond.

    Solution: Try adjusting the timeout on your health check settings.

  • Problem: Failing public key authentication.

    Cause: If you are using an HTTPS or SSL load balancer with back-end authentication enabled, the public key authentication will fail if the public key on the certificate does not match the public key configured on the load balancer.

    Solution: Check if your SSL certificate needs to be updated. If your SSL certificate is current, try re-installing the certificate on your load balancer.

Here's the guide which can help you to further troubleshoot Elastic Load Balancer: Troubleshoot Elastic Load Balancing

And Health Check in particular: Troubleshooting Elastic Load Balancing: Health Check Configuration