The kube-apiserver is the front door of the Kubernetes control plane and exposes the programmatic interface used to create, read, update, delete, and watch Kubernetes objects—so C is correct. Every interaction with cluster state ultimately goes through the Kubernetes API. Tools like kubectl, client libraries, GitOps controllers, operators, and core control plane components (scheduler and controllers) all communicate with the API server to submit desired state and to observe current state.
The API server is responsible for handling authentication (who are you?), authorization (what are you allowed to do?), and admission control (should this request be allowed and possibly mutated/validated?). After a request passes these gates, the API server persists the object’s desired state to etcd (the backing datastore) and returns a response. The API server also provides a watch mechanism so controllers can react to changes efficiently, enabling Kubernetes’ reconciliation model.
It’s important to distinguish this from the other options. etcd stores cluster data but does not expose the cluster’s primary user-facing API; it’s an internal datastore. kube-controller-manager runs control loops (controllers) that continuously reconcile resources (like Deployments, Nodes, Jobs) but it consumes the API rather than exposing it. kube-proxy is a node-level component implementing Service networking rules and is unrelated to the control-plane API endpoint.
Because Kubernetes is “API-driven,” the kube-apiserver is central: if it is unavailable, you cannot create workloads, update configurations, or even reliably observe cluster state. This is why high availability architectures prioritize multiple API server instances behind a load balancer, and why securing the API server (RBAC, TLS, audit) is a primary operational concern.
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