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Kubernetes Cluster Architecture – Complete Masterclass Notes

☸️ Kubernetes Cluster Architecture & Orchestration

Control Plane & Worker Node Topology, Pods vs Deployments, Services (ClusterIP, NodePort, LoadBalancer), Ingress Routing, ConfigMaps/Secrets, Rolling Updates aur Horizontal Pod Autoscaler (HPA) ka complete guide.

Module 01

1️⃣ What is Kubernetes (K8s) & Orchestration

Definition: Kubernetes (K8s) Google dwara open-source kiya gaya ek production-grade container orchestration platform hai. Yeh automated container scheduling, auto-scaling, self-healing, rolling deployments aur load-balancing manage karta hai.

Criteria Standalone Docker Kubernetes Cluster
Host Management Single physical server ya single VM tak limited. Hundreds ya thousands of heterogeneous nodes ka unified cluster pool.
Self-Healing Host crash hone par container restart nahi hota. Automatic Re-scheduling: Failed node ke pods turant doosre healthy nodes par shift ho jaate hain.
Scaling Manual docker run commands. Horizontal Pod Autoscaler (HPA): CPU/Memory spikes par automatically 3 se 30 pods scale karna.
Module 02

2️⃣ Control Plane & Worker Node Architecture

Subsystem Core Component Primary Responsibility
Control Plane (Master Node) kube-apiserver Cluster ka central entry point; saari REST API requests validate aur authenticate karta hai.
etcd Highly-available distributed key-value store jo cluster ka complete state persist karta hai.
kube-scheduler Naye pods ke resource requests inspect karke unhe best worker node par assign karta hai.
kube-controller-manager Reconciliation loops run karta hai (e.g. Desired state == Current state ensure karna).
Worker Node kubelet Node par running agent jo API server ke orders ke mutabiq containers start aur monitor karta hai.
kube-proxy Node-level network packet filtering aur service IP routing rules (iptables/IPVS) maintain karta hai.
CRI (Container Runtime) Low-level software (containerd, CRI-O) jo images pull karke containers execute karta hai.
Module 03

3️⃣ Core API Objects: Pods & Deployments

Pod: Kubernetes ka smallest deployable computing unit, jisme ek ya ek se zyada containers same network namespace (IP) aur storage share karte hain:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: jobs-api-deployment
  labels:
    app: jobs-api
spec:
  replicas: 3
  selector:
    matchLabels:
      app: jobs-api
  template:
    metadata:
      labels:
        app: jobs-api
    spec:
      containers:
      - name: api-server
        image: fresherjobsalert/jobs-api:v1.0.0
        ports:
        - containerPort: 8080
        resources:
          requests:
            memory: "128Mi"
            cpu: "250m"
          limits:
            memory: "256Mi"
            cpu: "500m"
Module 04

4️⃣ Kubernetes Services: Service Discovery

Pods ephemeral hote hain (restart par IP badal jata hai). Service pods ke group ke aage ek stable virtual IP aur DNS provide karta hai:

Service Type Scope & Routing Standard Use Case
ClusterIP (Default) Cluster ke andar accessible internal static IP. Internal microservices, backend databases, Redis caches.
NodePort Har worker node par static port (30000-32767) expose karta hai. Development testing, on-prem bare-metal internal access.
LoadBalancer Cloud provider (AWS NLB/ALB, Azure LB, GCP) ka public IP provision karta hai. Public customer-facing production internet traffic.
Live Kubernetes Deployment & HPA Scaling Simulator
[kubectl v1.31]: Cluster: production-k8s-aws | Context: ap-south-1 Active Deployment: 'jobs-api-deployment' | Replicas: 3/3 Running | Service: ClusterIP (10.96.0.45)
Module 05

5️⃣ Ingress Controllers & Path-Based Routing

Har service ke liye alag expensive cloud LoadBalancer khareedne ke bajay ek unified 7th-layer reverse proxy (NGINX Ingress/Traefik) use karna:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: main-ingress
  annotations:
    nginx.ingress.kubernetes.io/ssl-redirect: "true"
spec:
  rules:
  - host: api.fresherjobsalert.com
    http:
      paths:
      - path: /jobs
        pathType: Prefix
        backend:
          service:
            name: jobs-service
            port:
              number: 8080
      - path: /users
        pathType: Prefix
        backend:
          service:
            name: users-service
            port:
              number: 3000
Module 06

6️⃣ ConfigMaps, Secrets & Persistent Volumes

  • ConfigMap: Plaintext configuration variables aur properties files ko container image se separate rakhna.
  • Secret: Sensitive credentials (Base64 encoded) jaise database passwords aur TLS certificates inject karna.
  • PV & PVC (Persistent Volumes): Pod restart hone par bhi data safe rakhne ke liye cloud block storage (AWS EBS / Azure Disk) bind karna.
Module 07

7️⃣ Self-Healing & Horizontal Pod Autoscaling (HPA)

Zero-Downtime Rolling Update Strategy:
• maxSurge: 25% (Update ke dauran maximum kitne extra pods spawn ho sakte hain).
• maxUnavailable: 0% (Update ke dauran ek bhi purana pod tab tak destroy nahi hoga jab tak naya pod readinessProbe pass na kar le). 
# Horizontal Pod Autoscaler (HPA) CLI Command
kubectl autoscale deployment jobs-api-deployment --cpu-percent=75 --min=3 --max=20

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