ELB Health Check Repeatedly Fails

Question

I'm trying to set up an auto scaling group with application load balancer, but whenever I start it, the us-west-2b instance it creates gets stuck in a cycle of failing health checks (even though the instance passes status checks), deregistering and then creating a new instance to replace it, which then fails. The cycle continues and the only error code that I'm ever getting is the "Target.FailedHealthChecks" & "Health checks failed" reasons. I've tried going through the setup twice to make sure all my settings were correct and keep running into the same issue.

Gary Mclean EXPERT
5 months ago
Can you share your Target Group health settings and security group info masking any sensitive details? Security group info from the ALB and EC2s

Answer

First, check the security group and Network ACL settings on both the ELB and the instance to make sure all the ELBs subnets are able to communicate with the instances in 2b (and that the instance can send replies back)

If that's not the issue, to troubleshoot, disable ELB Healthchecks on the AutoScaling Group (ASG), by changing the healthcheck setting in the ASG to "EC2".  This way the instances won't be terminated when they fail healthchecks

Next, after an instance launches, SSH/RDP into it and check the webserver logs to see if any healthchecks from the ELB are making it in at all.  You can also launch a test instance in the same subnet(s) as the ELB (using the same security group) to try and send a curl to the instance in 2a to see if the connection can go through

ELB Health Check Repeatedly Fails

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