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Kubernetes (K8s) — Overview

What Is Kubernetes

Kubernetes is an open-source container orchestration platform that automates deploying, scaling, and managing containerized applications. Originally developed by Google and now maintained by the CNCF, it is the industry standard for production container management — 84% of enterprises run K8s in production (CNCF 2025).

Container Images ──► Kubernetes Cluster ──► Managed Pods (auto-healing, scaling)
Concept Description
Cluster A set of nodes (machines) that run containerized applications
Node A worker machine (physical or VM) that runs Pods
Pod Smallest deployable unit — one or more containers sharing network/storage
Deployment Declarative desired state for Pods — handles scaling, updates, rollbacks
Service Stable network endpoint that routes traffic to a set of Pods
Namespace Virtual cluster within a physical cluster for resource isolation

Kubernetes vs Docker Compose

Aspect Docker Compose Kubernetes
Scope Single host Multi-node cluster
Scaling Manual scale flag Auto-scaling (HPA, VPA)
Self-healing Restart policy only Pod replacement, rescheduling
Networking Single bridge network Cluster-wide CNI, Services, Ingress
Config mgmt .env files ConfigMaps, Secrets (base64; enable encryption at rest)
Rolling updates Recreate only Rolling, canary, blue-green
Production use Dev/test environments Production-grade orchestration

Architecture

┌─────────────── Control Plane ───────────────┐
│  kube-apiserver  ←→  etcd (state store)     │
│  kube-scheduler  ←→  controller-manager     │
│  cloud-controller-manager (optional)        │
└─────────────────────────────────────────────┘
           │ API calls
┌──────────┼──────────────────────────────────┐
│    Worker Node 1         Worker Node 2      │
│  ┌─────────────┐      ┌─────────────┐      │
│  │  kubelet     │      │  kubelet     │     │
│  │  kube-proxy  │      │  kube-proxy  │     │
│  │  ┌────┐┌────┐│     │  ┌────┐┌────┐│     │
│  │  │Pod1││Pod2││     │  │Pod3││Pod4││     │
│  │  └────┘└────┘│      │  └────┘└────┘│     │
│  └─────────────┘      └─────────────┘      │
└─────────────────────────────────────────────┘

Control Plane Components

Component Role
kube-apiserver REST API front-end; all components communicate through it
etcd Distributed key-value store holding all cluster state
kube-scheduler Assigns Pods to Nodes based on resources, affinity, taints
controller-manager Runs controllers (Deployment, ReplicaSet, Node, Job)

Node Components

Component Role
kubelet Agent on each node; ensures containers match Pod spec
kube-proxy Network proxy implementing Service routing rules
Container runtime containerd or CRI-O (Docker deprecated since v1.24)

Section Map

File Topics
01 — kubectl Fundamentals Commands, contexts, namespaces, output formats, aliases
02 — Workloads & Scheduling Pods, Deployments, StatefulSets, DaemonSets, Jobs, CronJobs
03 — Services & Networking ClusterIP, NodePort, LoadBalancer, Ingress, NetworkPolicies
04 — Configuration & Storage ConfigMaps, Secrets, PVs, PVCs, StorageClasses
05 — Helm & Deployment Strategies Helm charts, Kustomize, rolling update, canary, blue-green
06 — Security & Observability RBAC, Pod Security, Prometheus, Grafana, EFK, debugging

Quick Reference

Cluster Info

Task Command
Cluster info kubectl cluster-info
List nodes kubectl get nodes -o wide
All resources kubectl get all -A
API resources kubectl api-resources

Pod Lifecycle

Task Command
List pods kubectl get pods -o wide
Pod details kubectl describe pod <name>
Pod logs kubectl logs <pod> -f --tail=100
Shell into pod kubectl exec -it <pod> -- /bin/sh
Delete pod kubectl delete pod <name>

Deployments

Task Command
Create kubectl apply -f deployment.yaml
Scale kubectl scale deploy/<name> --replicas=3
Rollout status kubectl rollout status deploy/<name>
Rollback kubectl rollout undo deploy/<name>
History kubectl rollout history deploy/<name>

Debugging

Task Command
Events (sorted) kubectl get events --sort-by='.lastTimestamp'
Resource usage kubectl top pods -A
Debug pod kubectl debug -it <pod> --image=busybox
Port forward kubectl port-forward pod/<pod> 8080:80
Test DNS kubectl run tmp --rm -it --image=busybox -- nslookup <svc>

See also