custom health check vs elb health check

EC2 instance health check Elastic Load Balancer (ELB) health check Auto Scaling and Custom health checks Amazon EC2 performs automated checks on every running EC2 instance to identify hardware and software issues. Status checks are performed every minute and each returns a pass or a fail status.  If all checks pass, the overall status of the instance is OK.  If one or more checks fail, the overall status is impaired. Status checks are built into EC2, so they cannot be disabled or deleted. You can create or delete alarms that are triggered based on the result of the status checks. [...]