The administrator observes a "Pod Network Unreachable" health check failure in the NAI, specifically affecting several application pods on a newly…

The error messages FailedCreatePodSandBox and failed to set up network for sandbox are explicit indicators that the kubelet's request to the Container Network Interface (CNI) plugin to configure networking for a new pod has failed. Since the problem is isolated to a newly added worker node while existing nodes function correctly, it points to a localized issue with the CNI daemonset pod on that specific node. This CNI pod is responsible for IP address allocation and network interface creation for all application pods on its host. The most logical and direct troubleshooting step is to inspect the logs of this CNI pod to determine the cause of the failure.

A. A corrupted container runtime would likely manifest as a broader inability to start any container, not an error specifically isolated to network sandbox creation.
B. The kube-proxy service is responsible for implementing Kubernetes services (e.g., ClusterIP, NodePort), not for assigning IP addresses or creating network interfaces for individual pods.
C. While an underlying network misconfiguration could be the ultimate root cause, the CNI plugin is the component that directly interacts with it. The immediate failure is within the CNI, making its logs the primary source for diagnosis.

1. Nutanix Kubernetes Platform 4.1 Administration Guide: In the "Troubleshooting Kubernetes Clusters" section, under "Pod is Stuck in Pending State," the guide advises checking the status of system pods (including the CNI daemonset in the kube-system namespace) and using kubectl describe pod to check for events. The events listed in the question are characteristic of CNI failures, making the CNI pod the primary focus for investigation. (Reference: Nutanix Kubernetes Platform 4.1 Administration Guide, Chapter: "Troubleshooting," Section: "Troubleshooting Kubernetes Clusters").

2. Official Kubernetes Documentation: The Kubernetes documentation on troubleshooting states that pods stuck in Pending or ContainerCreating can be due to various reasons, including network plugin issues. The error FailedCreatePodSandBox specifically indicates a failure during the pod sandbox creation phase, where the container runtime calls the CNI plugin to set up the network. This confirms that the CNI is the failing component. (Reference: Kubernetes Documentation, Section: "Tasks > Troubleshoot > Troubleshoot Clusters > Default Network is not working").

3. Official Kubernetes Documentation: The documentation on Network Plugins explains that the kubelet on each node is responsible for invoking the CNI plugin to set up and tear down pod networking. A failure in this process, as seen on the new worker node, directly implicates the CNI plugin's operation on that specific node. (Reference: Kubernetes Documentation, Section: "Concepts > Extending Kubernetes > Compute, Storage, and Networking Extensions > Network Plugins").