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Difficulty: MediumElastic Load Balancing Health Checks and Troubleshooting

A company hosts a web application on Amazon EC2 instances in private subnets. The instances are registered with a target group of an Application Load Balancer (ALB) and are configured to listen on port 8080. A SysOps Administrator notices that the target group shows all registered instances as unhealthy with the status code HealthCodeMismatch. The Administrator verifies that the application is running and accessible locally on port 8080 on each instance, but the target group's health check is currently configured to use port 80 and the HTTP protocol. At the same time, the team reports that Amazon Route 53 failover is not triggering to the secondary disaster recovery region even when all primary ALB targets are unhealthy. Which two actions should the SysOps Administrator take to resolve these issues? (Select TWO.)

  1. Modify the target group's health check configuration to use port 8080 or the traffic port instead of port 80.Answer
  2. Set the 'Evaluate Target Health' parameter to 'Yes' on the Route 53 alias record pointing to the Application Load Balancer.Answer
  3. C
    Change the Route 53 routing policy to a simple routing policy and manually define a secondary failover IP address.
  4. D
    Update the target group health check configuration to point to the local loopback address (127.0.0.1) on port 80.
  5. E
    Configure the private subnets' Network Access Control List (NACL) to deny outbound traffic on ephemeral ports to the ALB.

Answer

Modify the target group's health check configuration to use port 8080 or the traffic port instead of port 80, and set the 'Evaluate Target Health' parameter to 'Yes' on the Route 53 alias record pointing to the Application Load Balancer.
To resolve the target group health check failures, the target group's health check port must match the port where the application is listening (port 8080 or the 'traffic-port'). To enable automatic Route 53 DNS failover when target instances become unhealthy, the Route 53 alias record pointing to the Application Load Balancer must have the 'Evaluate Target Health' setting enabled (set to Yes). This allows Route 53 to check the health status of the ALB and its registered targets before routing DNS traffic.

Step-by-Step Solution

1
Address the target group health check failure.
The target group's health check configuration is updated from port 80 to port 8080 (or the traffic-port) to align with the application listening port.
Since the application listens on port 8080 and nothing is running on port 80, health check queries sent to port 80 will fail. Updating this configuration allows the load balancer to reach the application.
2
Configure Route 53 DNS failover.
The 'Evaluate Target Health' parameter is enabled (set to Yes) on the Route 53 alias record pointing to the primary ALB.
By default, Route 53 does not check target health for alias records unless 'Evaluate Target Health' is set to Yes. Without this, Route 53 will continue routing traffic to the primary ALB even if all backend instances are unhealthy.

Key Concept

Elastic Load Balancing Health Checks and Route 53 Failover Integration
Estimated Time:2m 0s
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Topics

Elastic Load Balancing Health Checks and Troubleshooting

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