Some EC2 instances are reported as healthy by the Auto Scaling group but are marked unhealthy in the ALB target group. Which of the following is a likely cause?

The correct answer is that the target group's health check configuration uses the wrong port or path. If the Auto Scaling group (ASG) reports instances as healthy, it means the EC2 instance itself is running and passing basic checks. However, if the Application Load Balancer (ALB) marks them unhealthy, it indicates a problem with the application-level health check performed by the ALB's target group. This often happens when the health check is configured to ping an incorrect port or a non-existent path, causing it to fail even if the application is otherwise operational. Incorrect options: Security group rules blocking traffic would typically cause both the ASG and ALB to report issues, or at least prevent the ALB from ever reaching the instance. If the ASG health check type were set to EC2 status checks and the instances were failing, the ASG would mark them unhealthy, not healthy. EC2 instances failing to boot and not passing EC2 status checks would lead the ASG to mark them unhealthy, contradicting the premise.