> For the complete documentation index, see [llms.txt](https://bagus-cahyono.gitbook.io/programming-notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://bagus-cahyono.gitbook.io/programming-notes/cka/01_network.md). # Network Design Principles ![Kubernetes Network](https://kubernetes.io/docs/images/kubernetes-cluster-network.svg) *Source:* [*https://kubernetes.io/docs/concepts/cluster-administration/networking/#kubernetes-ip-address-ranges*](https://kubernetes.io/docs/concepts/cluster-administration/networking/#kubernetes-ip-address-ranges) ## Node Network The Node Network consists of Kubernetes worker nodes and control plane nodes. All nodes can communicate with each other. * Every node in the Kubernetes cluster should be able to communicate with every other node without NAT (Network Address Translation). * Kubernetes assumes a flat network where all nodes can talk freely. * Nodes usually have a routable IP address within the cluster. To see Nodes IP we can use command `kubectl get nodes -o wide`. ```bash ➜ kubectl get nodes -o wide NAME STATUS ROLES AGE VERSION INTERNAL-IP minikube Ready control-plane 19h v1.31.0 192.168.49.2 EXTERNAL-IP OS-IMAGE KERNEL-VERSION CONTAINER-RUNTIME Ubuntu 22.04.4 LTS 6.10.14-linuxkit docker://27.2.0 ``` ## Pod Network The Pod Network is where all Kubernetes pods communicate. Pods within the cluster communicate using direct IP routing. * Every pod gets a unique IP Address. * Every pod in a Kubernetes cluster gets a unique IP address. * Pod-to-pod communication happens directly without NAT. * The Container Network Interface (CNI) plugin is responsible for managing pod networking. * Container inside the same pod communicate by `localhost`. We can test pod to pod communication by `ping` from a pod to other pod. ```bash ➜ kubectl get pods -o wide NAME READY STATUS RESTARTS AGE postgres-f8f589d5b-59rw8 1/1 Running 0 4h37m simple-go-5dc4557ffc-c24fp 1/1 Running 0 4h8m simple-go-5dc4557ffc-d6tz6 1/1 Running 0 4h8m simple-go-5dc4557ffc-gv4fv 1/1 Running 0 4h8m IP NODE NOMINATED NODE READINESS GATES 10.244.0.11 minikube 10.244.0.17 minikube 10.244.0.15 minikube 10.244.0.16 minikube ``` ```bash ➜ kubectl exec -it simple-go-5dc4557ffc-c24fp -- ping 10.244.0.11 PING 10.244.0.11 (10.244.0.11): 56 data bytes 64 bytes from 10.244.0.11: seq=0 ttl=64 time=97.104 ms 64 bytes from 10.244.0.11: seq=1 ttl=64 time=0.219 ms 64 bytes from 10.244.0.11: seq=2 ttl=64 time=0.292 ms 64 bytes from 10.244.0.11: seq=3 ttl=64 time=0.160 ms 64 bytes from 10.244.0.11: seq=4 ttl=64 time=0.395 ms ^C --- 10.244.0.11 ping statistics --- 5 packets transmitted, 5 packets received, 0% packet loss round-trip min/avg/max = 0.160/19.634/97.104 ms ``` ## Service Network The Service Network is a virtual network used for Kubernetes Services. Services get a stable ClusterIP that does not change. Kubernetes load-balances traffic across backend pods. Kubernetes rewrites outbound traffic from a pod if it's destined for a Service.This ensures that the request is routed correctly to a backend pod. * Services use ClusterIP (virtual IP) to route traffic to pods. * kube-proxy manages service traffic using iptables or IPVS. Get service endpoints: ```bash ➜ kubectl get endpoints NAME ENDPOINTS AGE kubernetes 192.168.49.2:8443 24h postgres 10.244.0.11:5432 4h35m simple-go 10.244.0.15:8080,10.244.0.16:8080,10.244.0.17:8080 4h11m ``` ## References *