What scalability option does a Kubernetes controller implement when adding another pod replica in response to increased application load?

In the context of Kubernetes, when a controller adds another pod replica in response to increased application load, it is employing horizontal scaling. This means that the system accommodates more instances of the application (in this case, additional pods) to handle the increased load rather than enhancing the resources of an existing instance.

Horizontal scaling is particularly effective in cloud-native environments, such as those managed by Kubernetes, because it allows applications to maintain performance and responsiveness as demand fluctuates. With each additional pod, the application can distribute the incoming requests across multiple instances, providing better load balancing and redundancy. This is especially crucial in environments where application traffic can vary greatly.

The other options represent different scaling approaches. Vertical scaling would involve increasing the resources (CPU, RAM) of existing pods rather than adding new instances. Diagonal scaling is not a standard term in Kubernetes; it typically refers to a mix of vertical and horizontal scaling. Network scaling, while important, focuses on network infrastructure rather than directly on instances of application pods. Therefore, adding pod replicas to handle an increase in application load clearly aligns with horizontal scaling principles.