Networking Challenges¶

Container-to-Container inside Pods
Pod-to-Pod communication on the same node and across cluster nodes
Service-to-Pod communication within the same namespace and across cluster namespaces
External-to-Service communication for clients to access applications in a cluster

Container-to-Container¶

A network namespace can be shared: - across containers - with the host OS. Pause container creates network namespace for the Pod. Containers inside pod can talk to each other via localhost. 2023100715543131 K8s Single IP per Pod 2023100717075151 K8s CNI Each pod receives unique IP address(IP-per-Pod), like VMs are able to communicate with each other on the same network. Communication between containers must be throw Container network interface (CNI) supported by CNI plugins. Most CNI plugins are 3rd-party Software Defined Networking (SDN) solutions implementing the Kubernetes networking model. Examples of SDN: Flannel, Weave, Calico Pasted image 20230929202821.png

Pod-to-Pod Communication Across Nodes¶

The requirement from Kubernetes was the following: - All pods can communicate with each other across nodes. - All nodes can communicate with all pods. - No Network Address Translation (NAT). It can be achieved with: - - Weave - Flannel - Calico - Cilium. For more information see the "Cluster Networking"

External-to-Pod Communication¶

Kubernetes provides external accessibility through Services, which are sophisticated collections of network routing rules. These rules are stored in iptables on cluster nodes and executed by kube-proxy agents. By using kube-proxy to expose services, applications can be accessed from outside the cluster using a virtual IP address and a specific port number. This allows external users to interact with the applications hosted within the cluster.

The service object is used to connect to the Pods using: - in cluster: ClusterIP, - from outside of the cluster: NodePort or Load Balancer

2023100716443333 K8s Service network flow 1. LinuxFoundationX LFS158x. Chapter 4. Kubernetes Architecture 2. https://trainingportal.linuxfoundation.org/courses/kubernetes-for-developers-lfd259 Kubernetes Architecture