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Difficulty: EasyAuto Scaling and Elastic Load Balancing (ELB)

A solutions architect is configuring an Application Load Balancer (ALB) to distribute traffic to Amazon EC2 instances running a web service on custom port 80808080. The instances are managed by an Auto Scaling group. The solutions architect notices that the load balancer is marking all instances as unhealthy. The service is running on the instances, and security groups allow traffic on port 80808080. What is the most likely cause of this issue?

  1. A
    The security group on the EC2 instances does not allow outbound return traffic on port 80808080 because security groups are stateless.
  2. B
    Amazon Route 53 is using latency routing to direct health check traffic to the closest instance rather than using the load balancer.
  3. The target group health check is configured to query the default port 8080 instead of port 80808080.Answer
  4. D
    The Application Load Balancer is unable to perform health checks because target groups only support health checks on port 8080 or port 443443.

Answer

The target group health check is configured to query the default port 8080 instead of port 80808080.
The correct answer is correct because the web application listens on port 80808080, but the health check port is misconfigured to query the default port 8080. Since no service is listening on port 8080, the health checks fail and the instances are marked as unhealthy. Setting the health check port to 80808080 or utilizing the traffic port resolves the mismatch.

Step-by-Step Solution

1
Analyze the web service port configuration and health check behavior.
The web service runs on port 80808080, but if the health check is misconfigured to target port 8080, requests will fail since no service listens on port 8080.
Health checks must target a port where the application is listening to return a successful response.
2
Evaluate the statefulness of security groups.
Security groups are stateful, so outbound return traffic is automatically allowed.
Understanding security group statefulness helps rule out return-traffic blockages as a cause.
3
Identify Route 53 routing policy limitations.
Route 53 resolves client queries to the load balancer but does not perform target-level health check routing.
This rules out DNS routing policy misconfigurations.

Key Concept

ELB Target Group Health Check Port Configuration
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Topics

Auto Scaling and Elastic Load Balancing (ELB)

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