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Difficulty: EasyAuto Scaling and Elastic Load Balancing (ELB)

A solutions architect is deploying a web application on Amazon EC2 instances managed by an Auto Scaling group (ASG) behind an Application Load Balancer (ALB). The application runs on a custom port 8080. The security group of the EC2 instances allows inbound traffic only from the ALB's security group on port 8080. The solutions architect needs to configure the environment so that unhealthy instances are automatically detected and replaced by the ASG. Which TWO configurations should the solutions architect perform to meet these requirements? (Select TWO.)

  1. Configure the target group health check port to use the traffic port or port 8080.Answer
  2. Configure the Auto Scaling group to use Elastic Load Balancing (ELB) health checks.Answer
  3. C
    Keep the default target group health check port 80 and let the load balancer automatically forward the health checks to port 8080.
  4. D
    Modify the subnet's stateless Network ACL (NACL) to automatically track and allow return traffic from the load balancer's health checks.
  5. E
    Configure an Amazon Route 53 Latency routing policy to target the private IP addresses of the EC2 instances directly for health checks.

Answer

Configure the target group health check port to use the traffic port or port 8080, and configure the Auto Scaling group to use Elastic Load Balancing (ELB) health checks.
To ensure correct application health detection and automatic recovery, the Solutions Architect must perform two actions. First, the Application Load Balancer target group must perform health checks on the actual port where the application is listening (port 8080) because the security group blocks other ports such as the default port 80. Second, the Auto Scaling group must have its health check type set to 'ELB' so it can receive health check failures from the load balancer and automatically replace unhealthy instances.

Step-by-Step Solution

1
Align the Target Group health check port with the application's listening port.
The target group health checks are sent to port 8080, which is allowed by the security group and listened to by the web server.
By default, target groups run health checks on the traffic port or port 80. Since the custom application port is 8080 and security groups block port 80, the default checks would fail.
2
Enable ELB health checks in the Auto Scaling group configuration.
The Auto Scaling group receives health status updates from the Application Load Balancer target group.
By default, the ASG only uses EC2 status checks (hardware/system level). It must be explicitly configured to use ELB health checks so that application-level failures detected by the ALB prompt the replacement of unhealthy instances.

Key Concept

ELB health checks integrated with Auto Scaling groups for custom application ports.
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Topics

Auto Scaling and Elastic Load Balancing (ELB)

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