An administrator has deployed a web application on several Amazon EC2 instances behind an Application Load Balancer (ALB). After registering the instances with the target group, the administrator notices that all instances are reported as unhealthy by the load balancer. The application is configured to run on port 80. Which two configurations should the administrator verify to troubleshoot the failing health checks? (Select TWO.)
- The target group's health check port and path match the port and path where the web application is listening on the instances.Answer
- The security group associated with the EC2 instances allows inbound traffic on port 80 from the security group of the Application Load Balancer.Answer
- CThe Route 53 DNS record is configured with a failover routing policy that points to the load balancer rather than a simple routing policy.
- DThe target group's health check path points to a login page that requires basic authentication to verify user access control.
Answer
Verify that the target group's health check port and path match the application's configuration, and ensure that the security group of the EC2 instances allows inbound traffic on port 80 from the Application Load Balancer's security group.
For an Application Load Balancer to report instances as healthy, the security group on the EC2 instances must allow inbound traffic from the load balancer on the health check port. Additionally, the target group's health check configuration must specify a port and path that match the running web application so it receives a successful HTTP response (such as 200 OK).
Step-by-Step Solution
Key Concept
Application Load Balancer health checks require proper network connectivity (security groups) and correct application configuration (port and path) to successfully report targets as healthy.