Port 10250 (Kubelet)

Network port 10250 (TCP) is primarily associated with the Kubelet in Kubernetes. The Kubelet is the primary "node agent" that runs on each node in the cluster. Its role is to manage the containers running on that node. Port 10250 is used for the Kubelet's API server, which exposes various endpoints for querying node status, executing commands in containers, and retrieving logs. This API allows the Kubernetes control plane (specifically the API server) to communicate with and manage the Kubelet.

Technically, the Kubelet API server on port 10250 uses the HTTP protocol (often HTTPS with TLS enabled). The Kubernetes API server uses this port to send commands to the Kubelet, such as creating, starting, stopping, or deleting containers. The Kubelet then interacts with the container runtime (e.g., Docker, containerd, CRI-O) to execute these commands. This communication is bidirectional; the Kubelet also reports the status of the node and its containers back to the Kubernetes API server via this API. Authentication and authorization mechanisms, such as TLS certificates and authentication tokens, are crucial to secure this communication.

## Firewall Recommendations

The Kubelet API on port 10250 should be strictly firewalled to restrict access only from authorized sources, such as the Kubernetes API server and monitoring systems. Ideally, this port should not be exposed to the public internet. If external access is absolutely necessary, strong authentication and authorization mechanisms, such as TLS certificates and RBAC (Role-Based Access Control), must be implemented. Consider using network policies within the Kubernetes cluster to further restrict traffic to and from the Kubelet. Regularly audit and review firewall rules and authentication configurations to ensure they remain secure. Disable anonymous authentication and authorization modes. Use mutual TLS (mTLS) for enhanced security. Regularly update the Kubelet to the latest version to patch known vulnerabilities.