A web application runs on EC2 instances behind an Elastic Load Balancer, and during a traffic peak some instances begin failing health checks. What does the load balancer do once it marks an instance as unhealthy?
Show answer and explanation
Answer: B
The load balancer continuously runs health checks against its registered targets and maintains a queue of healthy ones. When a target fails its checks, the balancer removes it from rotation and spreads new requests across the remaining healthy targets, so user traffic is never sent to a failing host.
Busying itself with replacements is not the balancer's job — replacing failed instances is what an EC2 Auto Scaling group does, if one is attached.
Why the other options are wrong
- A. A load balancer neither terminates nor launches instances; that lifecycle work belongs to Auto Scaling.
- C. The balancer is independently redundant and stays in service; one or few unhealthy targets never take the whole balancer offline.
- D. Continuing to send production traffic to a failing host defeats the purpose of the health checks.