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Difficulty: MediumAuto Scaling and Elastic Load Balancing (ELB)

A financial services firm hosts a web application on Amazon EC2 instances in an Auto Scaling group (ASG). The instances are registered as targets in a target group for an Application Load Balancer (ALB). The application listens on TCP port 8080. The EC2 instance security group allows inbound traffic on TCP port 8080 from the ALB security group. However, the ALB health checks are failing, and the ALB is marking all instances as unhealthy. The systems administrator verifies that the application is running normally on the instances and accepting traffic. Which configuration change will resolve this issue?

  1. Update the target group health check settings to use port 8080 or the 'traffic-port' option.Answer
  2. B
    Configure the Application Load Balancer listener to perform health checks on port 80, and modify the instance security group to allow inbound traffic on port 80.
  3. C
    Modify the subnet Network ACL associated with the EC2 instances to permit outbound traffic on port 8080, because security groups are stateless and require explicit outbound rules.
  4. D
    Set up an Amazon Route 53 latency routing policy with health checks directed at the individual EC2 instance elastic IP addresses.

Answer

Update the target group health check settings to use port 8080 or the 'traffic-port' option.
The correct option is to update the target group health check settings to use port 8080 or the 'traffic-port' option. Since the application runs on port 8080, any health probe sent to a different port (such as the default port 80) will fail because no process is listening on that port. Aligning the health check port to the traffic port ensures the Application Load Balancer successfully probes the running application.

Step-by-Step Solution

1
Identify the application's listening port.
The application listens on TCP port 8080.
Health check probes must reach a port where the application is actively listening.
2
Analyze the load balancer target group configuration.
The target group is default-configured or misconfigured to probe a port other than 8080 (such as port 80).
If the ALB health check port does not match the application port, the health check fails.
3
Update the health check settings in the target group.
Setting the health check port to 8080 or 'traffic-port' restores successful health checks.
This aligns the load balancer's probes with the active application port, resolving the unhealthy status.

Key Concept

ELB Target Group Health Check Port Alignment
Estimated Time:1m 30s
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Topics

Auto Scaling and Elastic Load Balancing (ELB)

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