What is the primary advantage of using AWS Auto Scaling groups across multiple Availability Zones?

Correct answer: High availability and fault tolerance

Option A is correct because deploying Auto Scaling groups across multiple Availability Zones ensures that if one AZ experiences an outage, the instances in remaining AZs continue serving traffic, providing both high availability and fault tolerance without manual intervention. Option B is wrong because security configuration is not simplified by multi-AZ deployment; security groups, IAM roles, and network ACLs must still be designed and maintained regardless of the number of AZs used. Option C is wrong because spreading instances across AZs can actually increase cross-AZ data transfer costs, as AWS charges for data transferred between AZs; it does not inherently reduce transfer costs. Option D is wrong because database performance is determined by the database engine, instance sizing, and caching strategies, not by the AZ distribution of application-layer Auto Scaling groups.