A solutions architect needs to ensure that an Auto Scaling group launches instances across three Availability Zones equally. Which configuration achieves this?

Correct answer: Configure the Auto Scaling group with all three AZ subnets

Option C is correct because configuring an Auto Scaling group with subnets from all three Availability Zones is what instructs EC2 Auto Scaling where it may place instances, and the service will balance new launches across those AZs automatically using its rebalancing algorithm. Option A, enabling cross-zone load balancing on the ALB, affects how the load balancer distributes traffic to existing targets but does not control where Auto Scaling launches new instances. Option B, setting desired capacity to a multiple of 3, can help distribute instances evenly once the AZ subnets are configured, but without registering the subnets for all three AZs, instances will only launch in configured zones regardless of desired count. Option D, placement groups, are used to control physical hardware placement within a single AZ for low-latency or high-availability clustering and do not spread instances across multiple AZs.