The correct answer is kubelet.

The kubelet runs on every worker node as the node level agent and it watches the API server for Pod specifications and ensures the containers described in those Pods are started, monitored, and reported back to the control plane. The kubelet talks to the node's container runtime through the Container Runtime Interface and performs health checks and lifecycle management for containers on that node.

etcd is the cluster key value store that holds cluster state and configuration and it does not act as a node agent or start containers.

docker is a container runtime and not the Kubernetes node agent that monitors Pod specifications and manages container lifecycle. Note that the built in dockershim was removed in newer Kubernetes releases and runtimes now implement the CRI, so Docker is not the component responsible for the behavior described.

kubectl is a client command line tool used to interact with the API server and it does not run on worker nodes to manage or monitor containers.

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