An Application Load Balancer fronts an Auto Scaling group, and the team wants unhealthy instances to be replaced automatically rather than just removed from rotation. They configure the Auto Scaling group health check type so the group acts on the load balancer's view of each instance. Which setting makes the Auto Scaling group replace instances that the load balancer reports as unhealthy?
- AKeep the default EC2 health check type, since it already reflects whether the application is responding to load balancer requests.
- BSet the Auto Scaling group health check type to ELB so it uses the load balancer target health to decide which instances to replace. Correct
- CEnable connection draining on the load balancer so in-flight requests finish before the group replaces a failing instance automatically.
- DLower the load balancer health check interval so failing instances are detected sooner and the group reacts to them more quickly.
Why A is wrong: The default EC2 health check only covers instance and system status, so an instance failing application health checks at the load balancer is still considered healthy and is not replaced.
Why B is correct: Setting the health check type to ELB makes the Auto Scaling group treat targets the load balancer marks unhealthy as failed, so it terminates and replaces them automatically.
Why C is wrong: Connection draining controls how existing connections complete during deregistration, but it does not change which instances the Auto Scaling group decides to replace.
Why D is wrong: A shorter interval speeds detection at the load balancer, but unless the group uses ELB health, it never acts on that status to replace the instance.