How does CNI (Container Network Interface) work in Kubernetes?

CNI (Container Network Interface) is a specification and a set of plugins that Kubernetes uses to configure network interfaces for containers.

How CNI works in Kubernetes:

1. When kubelet starts a pod, it calls CNI plugins to set up the network.
2. CNI plugins create and configure a network interface inside the container, connecting it to the cluster network.
3. The plugin allocates an IP address for the container and sets up routing.
4. After successful configuration, the container gains network access according to the cluster policy.

CNI divides responsibilities:

• Kubernetes manages the lifecycle of pods and calls CNI.
• CNI plugins implement specific network solutions (Calico, Flannel, Weave, etc.).

Thus, CNI provides a standardized way to connect containers to the network, allowing different network technologies to be used without changing Kubernetes.