An Auto Scaling group behind an ALB keeps unhealthy instances in service — the app returns 500s but the ASG health check still reports the instances healthy. What fixes the detection gap?
A.Reduce the ASG min size
Min size changes capacity, not health detection.
B.Change the ASG health check type to ELB so load balancer failures trigger replacement
Correct. ELB health checks surface application failure to the ASG.
C.Increase instance size so the app stops failing
Bigger instances mask symptoms; the health gap remains.
D.Attach a second target group
A second target group doesn't change ASG health evaluation.
Why this answer
Default ASG health checks use EC2 status only — an instance can pass while the app is dead. Setting the health check type to ELB lets the load balancer's app-level health checks mark instances unhealthy, so the ASG replaces them.
Correct answer: B · Last reviewed 2026-10-26
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