The correct answer is container runtime.

container runtime on each worker node is responsible for pulling container images and starting the container processes. The runtime implements the Container Runtime Interface and performs low level functions such as image management, container creation, and process isolation. Common examples are containerd and CRI-O and they run on the node to manage containers when the kubelet requests actions.

kubelet runs on every node and acts as the node agent that watches the API server and enforces pod specifications. It does not itself perform the low level image pulls and process creation. Instead kubelet instructs the container runtime to carry out those actions and then monitors the container state.

scheduler runs in the control plane and decides which node should host a pod based on constraints and resource availability. It does not run on worker nodes and it does not perform image pulls or start processes on the node.

API server is the central control plane component that exposes the Kubernetes API and stores cluster state. It handles API requests and validation but it does not pull container images or launch processes on worker nodes.

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