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Difficulty: EasyElastic Load Balancing Health Checks and Troubleshooting

A target group for an Application Load Balancer (ALB) contains EC2 instances that are all marked as unhealthy. Although the web application is running properly and listening on port 80 on all instances, the target group's health check is configured to query port 8080. Which configuration change will resolve this issue?

  1. Modify the target group's health check settings to use port 80 or the traffic port.Answer
  2. B
    Modify the subnet's network access control list (NACL) rules to allow outbound traffic from ephemeral ports to port 8080.
  3. C
    Add a route to the Internet Gateway in the subnet's route table to allow the instances to communicate with the health check service.
  4. D
    Change the Amazon Route 53 routing policy for the primary domain to failover routing so traffic bypasses the unhealthy target group.

Answer

Modify the target group's health check settings to use port 80 or the traffic port.
Modifying the target group's health check settings to use port 80 (or the traffic port) allows the load balancer to query the port where the web application is actually listening. Since the application is running properly on port 80, this change will allow the health checks to succeed, marking the instances as healthy.

Step-by-Step Solution

1
Identify the port on which the web application is listening on the EC2 instances.
The application is listening on port 80.
Health check requests must be sent to the port where the application is listening to receive a valid response.
2
Identify the port that the Application Load Balancer target group is currently querying for health checks.
The target group is querying port 8080.
Since the application is not listening on port 8080, health checks will fail.
3
Update the health check port in the target group configuration to match the application port.
The health check port is changed to port 80 (or 'traffic port').
This aligns the health check destination with the listening application service, allowing the health checks to succeed.

Key Concept

Target Group Health Check Configuration
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Topics

Elastic Load Balancing Health Checks and Troubleshooting

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