CNI: Container Network Interface in Depth

The node shows NotReady. The kubelet is running. But pods won't schedule — stuck in ContainerCreating with network errors. Is it the CNI plugin binary? A cniVersion mismatch? The IPAM plugin failing to allocate? Knowing the CNI architecture cuts diagnosis from 30 minutes to 3.

Since Kubernetes 1.24, CNI is the container runtime's responsibility — kubelet no longer has --cni-bin-dir or --network-plugin flags. This article covers the spec, plugin chaining, real Flannel and Calico configs, and the gotchas that break pod networking.