☸️ KUBERNETES BASIC

☸️ Kubernetes (K8s) – Complete Core Notes

Container Orchestration Architecture, Cluster Nodes, Pods Lifecycle, Deployments, Declarative YAML aur Kubectl CLI ka comprehensive reference guide.

1️⃣ Kubernetes Kya Hai?

Definition: Kubernetes (jise K8s bhi kaha jata hai) ek open-source container orchestration platform hai jise Google ne develop kiya tha. Yeh hazaron containers ko automatically deploy, scale, balance aur manage karta hai.

Docker vs Kubernetes Concept: Docker ka kaam application ko single container package ke roop me build aur run karna hota hai, jabki Kubernetes un hazaron distributed Docker containers ko multiple servers (clusters) par coordinate aur manage karta hai.

• Container Orchestration: Containerized applications ke deployment aur networking ko automate karta hai.
• Auto-Scaling: Web traffic badhne par automatically new pods spawn karta hai aur traffic kam hone par scale-down kar deta hai.
• Self-Healing: Agar koi container ya pod crash ho jaye, toh K8s use bina human intervention ke instantly restart ya replace kar deta hai.

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2️⃣ Kubernetes Ke Core Features

• Automated Rollouts & Rollbacks: Application me changes bina kisi downtime ke deploy ho jate hain; error aane par turant pichhle version par rollback ho jata hai.
• Service Discovery & Load Balancing: Har pod ko unique IP aur single DNS name assign karta hai aur incoming network traffic ko pods me distribute karta hai.
• Storage Orchestration: Local storage, public cloud storage (AWS EBS, GCP PD) ko automatically pods ke sath mount karta hai.
• Secret & Configuration Management: Passwords, API keys aur configurations ko bina container image dobara build kiye securely store aur update karta hai.

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3️⃣ Kubernetes Cluster Architecture Components

Component	Role & Architectural Layer	Description
Cluster	High-level Environment	Master (Control Plane) aur Worker Nodes ka collective group.
Control Plane (Master)	Management Brain	Cluster decisions (Scheduling, event response, cluster state) manage karta hai.
Node (Worker Machine)	Physical / Virtual Server	Actual physical server ya cloud VM jahan applications run hoti hain.
Pod	Smallest Execution Unit	Ek ya ek se zyada containers ka group jo shared storage aur network IP use karte hain.
Deployment	Declarative Controller	Pods ke desired number of replicas aur rolling updates ko maintain karta hai.
Service	Networking Abstraction	Dynamic pods ke group ko stable IP address aur DNS provide karke expose karta hai.

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4️⃣ Essential Kubectl CLI Commands

Kubernetes cluster se interact karne ke liye kubectl command line tool use kiya jata hai:

Command	Syntax Preview	Kaam / Purpose
kubectl get nodes	kubectl get nodes -o wide	Cluster me judhe sabhi active nodes ka status dekhna.
kubectl get pods	kubectl get pods -A	Cluster me running pods ki list aur unka health status dekhna.
kubectl apply	kubectl apply -f deployment.yaml	YAML configuration file se resources create ya update karna.
kubectl describe	kubectl describe pod <pod-name>	Kisi specific pod ke detailed events aur logs troubleshoot karna.
kubectl delete	kubectl delete pod <pod-name>	Kisi running resource ko terminate/delete karna.
kubectl logs	kubectl logs -f <pod-name>	Container ke live application logs terminal par stream karna.

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5️⃣ Deploying a Container (Declarative YAML)

Kubernetes me resources hamesha declarative YAML files ke zariye define aur apply kiye jaate hain:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-app-deployment
  labels:
    app: web-app
spec:
  replicas: 3
  selector:
    matchLabels:
      app: web-app
  template:
    metadata:
      labels:
        app: web-app
    spec:
      containers:
      - name: web-container
        image: nginx:latest
        ports:
        - containerPort: 80

Configuration apply karne ke liye run karein:

kubectl apply -f deployment.yaml

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6️⃣ Scaling Pods & Self-Healing Simulation

Traffic demand ke hisab se CLI ya file se instances scale kiye jaate hain:

kubectl scale deployment web-app-deployment --replicas=5

Live Replica Pods Scaling Simulator

Replicas: 3

$ kubectl scale deployment web-app-deployment --replicas=3
deployment.apps/web-app-deployment scaled [3/3 pods healthy]

Self-Healing Architecture: Agar aap kisi pod ko kubectl delete pod se manually kill bhi kar denge, toh Deployment controller turant 1 naya pod start kar dega taaki total replica count hamesha barabar rahe.