Will setting health check to ELB instead of EC2 ignore EC2 metrics like CPU Utilization?

Question

If the autoscaling group's health check type is set to ELB then it will automatically remove any instances that fail the ELB health checks ( set in the healthcheck URL )

As long as the configured health check properly reports than an instance is bad (which sounds like it is the case since you say ELB is marking the instance as unhealthy) this should work, but does this mean other autoscaling triggers like CPU Utilization ( set in Configuration->Scaling->Scaling Trigger) be ignored?

Answer 1

• Autoscaling group will not health check to ELB and vice versa.
• ELB will check the health status of registered EC2 instances. ELB will continuously ping EC2 instance with specific port and specific page example port 80 and index.html page for every time period say 30 seconds or 60 seconds.
• If any one of the registered instance is unhealthy then ELB will not send traffic to those instances and will not terminate or stop EC2 instances. ELB continuously check health status of EC2 instances which is registered in ELB.
• If an unhealthy instance become healthy then ELB will send traffic to an instance.
• AutoScaling group will health check to EC2 instances same like ELB do. But in AutoScaling group, if an EC2 instance goes to stopped state then it will terminate from the group and launch new instances with same configurations.
• If Autoscaling group is integrated with ELB, newly added instance in the group will be added to ELB dashboard.

Health check cannot be done with ELB. You can monitor ELB using AWS CloudWatch logs and upload to target S3 bucket. You can enable monitoring feature in ELB and provide your target S3 bucket to store the logs.