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Difficulty: EasyAuto Scaling and Elastic Load Balancing (ELB)

A company hosts a web application on Amazon EC2 instances inside an Auto Scaling group behind an Application Load Balancer (ALB). The application on one of the EC2 instances becomes unresponsive, causing the ALB target group health check to mark that instance as unhealthy. However, the Auto Scaling group does not terminate or replace the unhealthy instance. Which action will ensure that the Auto Scaling group automatically replaces the unresponsive instance?

  1. A
    Modify the subnet Network Access Control List (NACL) to allow inbound ephemeral port traffic.
  2. B
    Update the Application Load Balancer target group health check configuration to query a different port than the application port.
  3. Change the health check type of the Auto Scaling group from EC2 to ELB.Answer
  4. D
    Configure an Amazon Route 53 latency routing policy to redirect client traffic away from the unresponsive instance.

Answer

Change the health check type of the Auto Scaling group from EC2 to ELB.
Changing the health check type of the Auto Scaling group from EC2 to ELB enables the group to utilize the load balancer's application-level health checks. When the Application Load Balancer target group marks the unresponsive instance as unhealthy, the Auto Scaling group detects this status, terminates the failed instance, and launches a new, healthy instance to maintain the desired capacity.

Step-by-Step Solution

1
Diagnose why the Auto Scaling group fails to act on application-level failures.
Identify that the Auto Scaling group's default health check type is 'EC2', which only checks hardware and hypervisor status, leaving it unaware of application-level health check failures reported by the load balancer.
EC2 status checks do not monitor the status of the web application or service running on the instances.
2
Select the configuration that integrates Auto Scaling lifecycle events with Elastic Load Balancing health status.
Determine that changing the Auto Scaling group health check type to 'ELB' allows the group to consume target group health status.
When the health check type is set to 'ELB', the Auto Scaling group marks an instance as unhealthy and replaces it if either the EC2 status checks or the ELB target group health checks fail.

Key Concept

Auto Scaling Group Health Check Integration with Elastic Load Balancing
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Topics

Auto Scaling and Elastic Load Balancing (ELB)

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