Kubernetes Network Architecture and Container Network Interface (CNI) Overview

This article provides a comprehensive overview of Kubernetes network architecture and related components. It begins by explaining Kubernetes network fundamentals, including bridge and overlay network models, and how containers communicate within shared networks or across host nodes. The article covers Kubernetes network APIs such as Service, Endpoint, and NetworkPolicy, and mentions third-party plugins like Flannel, Calico, and Weave Net.

The Container Network Interface (CNI) section explains how CNI provides a standardized API for managing container networks, creating resources like MAC addresses, IP addresses, and routes, and supporting different network models. It also covers network security features including policies, authentication, and encryption.

Practical examples are provided for creating NetworkPolicy configurations to control traffic between pods, and Ingress rules to route HTTP requests to services. The article then details specific CNI plugins:

Flannel is described as an open-source CNI plugin using VXLAN technology for overlay networks, with automatic IP address allocation. Installation examples include applying YAML configurations and setting environment variables like FLANNEL_SUBNET_FILE.

Calico is presented as a network solution providing security and isolation using BGP and IPAM technologies. The installation process includes applying RBAC configurations and creating network policies, with examples of default-deny policies.

The article covers Kubernetes service discovery, explaining how Services provide virtual IP addresses and load balancing for groups of pods. It details Service types (ClusterIP, NodePort, LoadBalancer, ExternalName) and provides YAML examples for creating services and ingress objects.

Kubernetes DNS is explained using KubeDNS or CoreDNS for name resolution within clusters, with deployment examples and configuration files.

Ingress controllers are discussed, including Nginx Ingress Controller installation via Helm and configuration examples. The article also covers Traefik deployment with namespace creation, YAML configuration download, and ingress rule setup.

Throughout the article, practical code examples demonstrate how to configure and deploy various network components in Kubernetes environments.