A company uses infrastructure as code (IaC) to provision Amazon EC2 instances.

Comprehensive and Detailed Explanation From Exact Extract:

D is required because the only reliable way to ensure newly launched Auto Scaling instances are patched is to make the launch template reference an AMI that already includes the latest security updates (an immutable image approach). AWS Systems Manager can automate building and maintaining patched AMIs (for example, through automated image creation workflows), after which the launch template is updated to the new AMI and the fleet is updated using Instance Refresh. Instance Refresh performs a controlled rolling replacement of instances so that the Auto Scaling group converges to the new AMI baseline.

C complements D by ensuring safe replacement and availability during the refresh/replacement process. Placing an ALB in front of the Auto Scaling group with health checks ensures that only healthy, fully bootstrapped/patched instances receive traffic, and that traffic is drained away from instances being replaced. Monitoring target health confirms the rollout is successful and minimizes risk during patch-driven reboots or instance replacement.

Why the other options are incorrect:

A: A termination policy setting does not ensure new instances are patched. It only affects which instances are terminated first. It does not solve the “launch patched instances” requirement.

B: Running two Auto Scaling groups and continuing in-place patching increases operational overhead and still risks drift and unpatched capacity when scaling occurs outside the maintenance window. It also does not address the core issue: the launch template AMI baseline.

E: NLB + termination protection does not ensure instances are patched at launch. Termination protection can interfere with Auto Scaling’s ability to replace instances, and NLB does not inherently provide the same application-layer health check behavior and deployment safety patterns typically used for rolling replacements (compared to ALB target group health checks).