An overlay network provides a virtual network on top of an existing physical network, giving Kubernetes pods connectivity without requiring a dedicated physical address for every pod. A VXLAN encapsulates Layer 2 traffic over Layer 3 and adds headers that help route packets between nodes. section 6.5
Kubernetes commonly implements the overlay through the Container Network Interface (CNI). A CNI plugin runs as a DaemonSet, creates a virtual network interface in each node’s root namespace, and mediates packet flow into and out of the node. section 6.5
For Kubernetes administration and CKA preparation:
- Recognize Flannel and Calico as relevant CNI choices; Kindnet is used by kind clusters. section 6.5
Verify the overlay DaemonSet
Run kubectl get ds -n kube-system and confirm the CNI DaemonSet has desired, current, ready, and available instances on the nodes. A kind cluster reports kindnet; a Flannel installation reports kube-flannel pods running across nodes.
