What is the primary reason for spreading resources among different availability zones?

Spreading resources among different availability zones primarily serves the purpose of improving the overall reliability and availability of applications and services. By distributing resources across multiple availability zones, which are physically separated locations within a region, you can ensure that your applications continue to operate even in the event of a failure in one zone.

Availability zones are designed to be isolated from failures in other zones. When you deploy resources like EC2 instances, databases, and load balancers across different availability zones, you protect against data loss and application downtime that could occur if there were an issue impacting a single zone. This strategy enhances fault tolerance and ensures that your applications can achieve high availability.

Considering the context of the other choices: avoiding unbalanced traffic is an operational concern but does not encompass the primary goal of spreading resources. Keeping capacity balanced between data centers can be important, but the overarching reason remains on reliability. Enhancing network performance is a potential outcome, but it is secondary to the main reason of ensuring high availability and fault tolerance. The central concept revolves around spreading resources among zones to safeguard against localized disruptions, thus promoting service continuity.