Kubernetes Networking

Question 1

How are pods connected regarding networking, ip-address and communication in Kubernetes?

Answer 1

• Kubernetes assigns a unique IP address to each Pod
• Containers in a pod share the same ip-address, because they share the same namespace
• thus they can refer to each other by localhost
• Containers in a pod can expose unique ports and become accessible through the same pod-IP

Question 2

In addition to Container Network Interface, what requirements need to be fulfilled by networking driver developers in Kubernetes?

Answer 2

• all pods on a node can communicate with all pods on all nods without Network Address Translation (NAT)
• Agents on a node (kubelet, system daemons, …) can communicate with all pods on that node
• the pods in the host-network of a node can communicate with all pods on all nodes without NAT

Question 3

What are projects implementing the Kubernetes CNI and what do they build?

Answer 3

• are in fact Software Defined Networking Implementations
• which are deployed on a Kubernetes Cluster as plugins
• that build a private, virtual, isolated network layer for Pod-to-Pod communication

Question 4

What are examples for CNI-implementations?

Answer 4

• Azure CNI for Kubernetes
• Calico
• Cilium
• Flannel