Which of the following is NOT a component of the master node in a Kubernetes cluster?

The correct choice identifies Kubelet as not being a component of the master node in a Kubernetes cluster. Instead, Kubelet is an agent that runs on each worker node in the cluster. Its primary function is to communicate with the master node and ensure that the containers are running in the pods as specified by the cluster's desired state.

In contrast, the other components mentioned - Scheduler, Controller, and API Server - are all integral parts of the master node.

The Scheduler is responsible for assigning work to worker nodes based on resource availability and other scheduling policies. The Controller manages the state of the cluster by watching for changes and taking the necessary actions to maintain the desired state of the system. The API Server serves as the central management entity that exposes the Kubernetes API and acts as a gateway for all communications within the cluster, allowing components to communicate effectively.

Thus, recognizing the roles of these components underscores the distinction between what constitutes the master node and other nodes in a Kubernetes architecture.