Kubernetes — pods, deployments & services (intro)

Introduction to Kubernetes

Kubernetes (K8s) is a container orchestration platform that automates deployment, scaling, and management of containerized applications across clusters of machines.

Core Kubernetes Concepts

Pods - Smallest Deployable Units

yaml

# pod.yaml - Basic Pod configuration
apiVersion: v1
kind: Pod
metadata:
  name: nginx-pod
  labels:
    app: nginx
spec:
  containers:
  - name: nginx
    image: nginx:1.21
    ports:
    - containerPort: 80
    resources:
      requests:
        memory: "64Mi"
        cpu: "250m"
      limits:
        memory: "128Mi"
        cpu: "500m"

Deployments - Managing Pod Replicas

yaml

# deployment.yaml - Deployment configuration
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.21
        ports:
        - containerPort: 80
        env:
        - name: ENV
          value: "production"
        livenessProbe:
          httpGet:
            path: /
            port: 80
          initialDelaySeconds: 30
          periodSeconds: 10
        readinessProbe:
          httpGet:
            path: /
            port: 80
          initialDelaySeconds: 5
          periodSeconds: 5

Services - Exposing Applications

yaml

# service.yaml - Service configuration
apiVersion: v1
kind: Service
metadata:
  name: nginx-service
spec:
  selector:
    app: nginx
  ports:
  - protocol: TCP
    port: 80
    targetPort: 80
  type: LoadBalancer  # ClusterIP, NodePort, LoadBalancer

Complete Web Application Example

Frontend Deployment

yaml

# frontend-deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: frontend
  labels:
    tier: frontend
spec:
  replicas: 2
  selector:
    matchLabels:
      app: frontend
  template:
    metadata:
      labels:
        app: frontend
        tier: frontend
    spec:
      containers:
      - name: react-app
        image: myregistry/frontend:v1.0.0
        ports:
        - containerPort: 3000
        env:
        - name: REACT_APP_API_URL
          value: "http://backend-service:8000"
        resources:
          requests:
            memory: "256Mi"
            cpu: "250m"
          limits:
            memory: "512Mi"
            cpu: "500m"

---
# Frontend Service
apiVersion: v1
kind: Service
metadata:
  name: frontend-service
spec:
  selector:
    app: frontend
  ports:
  - port: 80
    targetPort: 3000
  type: LoadBalancer

Backend Deployment

yaml

# backend-deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: backend
  labels:
    tier: backend
spec:
  replicas: 3
  selector:
    matchLabels:
      app: backend
  template:
    metadata:
      labels:
        app: backend
        tier: backend
    spec:
      containers:
      - name: api-server
        image: myregistry/backend:v1.0.0
        ports:
        - containerPort: 8000
        env:
        - name: DATABASE_URL
          valueFrom:
            secretKeyRef:
              name: db-secret
              key: url
        - name: REDIS_URL
          value: "redis://redis-service:6379"
        livenessProbe:
          httpGet:
            path: /health
            port: 8000
          initialDelaySeconds: 30
          periodSeconds: 10
        readinessProbe:
          httpGet:
            path: /ready
            port: 8000
          initialDelaySeconds: 5
          periodSeconds: 5

---
# Backend Service
apiVersion: v1
kind: Service
metadata:
  name: backend-service
spec:
  selector:
    app: backend
  ports:
  - port: 8000
    targetPort: 8000
  type: ClusterIP

Database Deployment

yaml

# postgres-deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: postgres
spec:
  replicas: 1
  selector:
    matchLabels:
      app: postgres
  template:
    metadata:
      labels:
        app: postgres
    spec:
      containers:
      - name: postgres
        image: postgres:15
        env:
        - name: POSTGRES_DB
          value: "myapp"
        - name: POSTGRES_USER
          valueFrom:
            secretKeyRef:
              name: db-secret
              key: username
        - name: POSTGRES_PASSWORD
          valueFrom:
            secretKeyRef:
              name: db-secret
              key: password
        ports:
        - containerPort: 5432
        volumeMounts:
        - name: postgres-storage
          mountPath: /var/lib/postgresql/data
      volumes:
      - name: postgres-storage
        persistentVolumeClaim:
          claimName: postgres-pvc

---
# Database Service
apiVersion: v1
kind: Service
metadata:
  name: postgres-service
spec:
  selector:
    app: postgres
  ports:
  - port: 5432
    targetPort: 5432
  type: ClusterIP

ConfigMaps and Secrets

ConfigMap for Configuration

yaml

# configmap.yaml
apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  app.properties: |
    debug=true
    log_level=info
    max_connections=100
  nginx.conf: |
    server {
      listen 80;
      location / {
        proxy_pass http://backend-service:8000;
      }
    }

Secret for Sensitive Data

yaml

# secret.yaml
apiVersion: v1
kind: Secret
metadata:
  name: db-secret
type: Opaque
data:
  username: dXNlcg==  # base64 encoded 'user'
  password: cGFzcw==  # base64 encoded 'pass'
  url: cG9zdGdyZXNxbDovL3VzZXI6cGFzc0Bwb3N0Z3Jlcy1zZXJ2aWNlOjU0MzIvbXlhcHA=

Persistent Storage

yaml

# persistent-volume.yaml
apiVersion: v1
kind: PersistentVolume
metadata:
  name: postgres-pv
spec:
  capacity:
    storage: 10Gi
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  hostPath:
    path: /data/postgres

---
# Persistent Volume Claim
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: postgres-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 10Gi

Ingress for External Access

yaml

# ingress.yaml
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: app-ingress
  annotations:
    nginx.ingress.kubernetes.io/rewrite-target: /
    cert-manager.io/cluster-issuer: "letsencrypt-prod"
spec:
  tls:
  - hosts:
    - myapp.example.com
    secretName: myapp-tls
  rules:
  - host: myapp.example.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: frontend-service
            port:
              number: 80
      - path: /api
        pathType: Prefix
        backend:
          service:
            name: backend-service
            port:
              number: 8000

Essential kubectl Commands

bash

# Cluster information
kubectl cluster-info
kubectl get nodes
kubectl describe node node-name

# Working with resources
kubectl get pods
kubectl get deployments
kubectl get services
kubectl get all

# Detailed information
kubectl describe pod pod-name
kubectl describe deployment deployment-name

# Logs and debugging
kubectl logs pod-name
kubectl logs -f deployment/backend  # Follow logs
kubectl exec -it pod-name -- /bin/bash

# Apply configurations
kubectl apply -f deployment.yaml
kubectl apply -f .  # Apply all YAML files in directory

# Delete resources
kubectl delete pod pod-name
kubectl delete deployment deployment-name
kubectl delete -f deployment.yaml

# Scale deployments
kubectl scale deployment nginx-deployment --replicas=5

# Port forwarding (for testing)
kubectl port-forward service/backend-service 8080:8000

Deployment Strategies

Rolling Update

yaml

# Rolling update strategy (default)
apiVersion: apps/v1
kind: Deployment
metadata:
  name: rolling-update-app
spec:
  replicas: 4
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxSurge: 1        # Max extra pods during update
      maxUnavailable: 1  # Max unavailable pods during update
  template:
    # ... pod template

Blue-Green Deployment

yaml

# Blue deployment
apiVersion: apps/v1
kind: Deployment
metadata:
  name: app-blue
  labels:
    version: blue
spec:
  replicas: 3
  selector:
    matchLabels:
      app: myapp
      version: blue
  template:
    metadata:
      labels:
        app: myapp
        version: blue
    spec:
      containers:
      - name: app
        image: myapp:v1.0.0

---
# Green deployment  
apiVersion: apps/v1
kind: Deployment
metadata:
  name: app-green
  labels:
    version: green
spec:
  replicas: 3
  selector:
    matchLabels:
      app: myapp
      version: green
  template:
    metadata:
      labels:
        app: myapp
        version: green
    spec:
      containers:
      - name: app
        image: myapp:v2.0.0

---
# Service switches between blue and green
apiVersion: v1
kind: Service
metadata:
  name: app-service
spec:
  selector:
    app: myapp
    version: blue  # Change to 'green' for deployment
  ports:
  - port: 80
    targetPort: 8000

Monitoring and Health Checks

yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: healthy-app
spec:
  replicas: 3
  selector:
    matchLabels:
      app: healthy-app
  template:
    metadata:
      labels:
        app: healthy-app
    spec:
      containers:
      - name: app
        image: myapp:latest
        ports:
        - containerPort: 8000
        
        # Liveness probe - restart if fails
        livenessProbe:
          httpGet:
            path: /health
            port: 8000
          initialDelaySeconds: 30
          periodSeconds: 10
          timeoutSeconds: 5
          failureThreshold: 3
          
        # Readiness probe - remove from service if fails
        readinessProbe:
          httpGet:
            path: /ready
            port: 8000
          initialDelaySeconds: 5
          periodSeconds: 5
          timeoutSeconds: 3
          failureThreshold: 3
          
        # Startup probe - for slow starting applications
        startupProbe:
          httpGet:
            path: /startup
            port: 8000
          initialDelaySeconds: 10
          periodSeconds: 10
          failureThreshold: 10

Namespace Organization

yaml

# namespace.yaml
apiVersion: v1
kind: Namespace
metadata:
  name: production
  labels:
    env: production

---
# Deploy to specific namespace
apiVersion: apps/v1
kind: Deployment
metadata:
  name: app
  namespace: production  # Specify namespace
spec:
  # ... deployment spec

Resource Management

yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: resource-managed-app
spec:
  replicas: 3
  selector:
    matchLabels:
      app: resource-app
  template:
    metadata:
      labels:
        app: resource-app
    spec:
      containers:
      - name: app
        image: myapp:latest
        resources:
          requests:        # Guaranteed resources
            memory: "256Mi"
            cpu: "250m"
          limits:          # Maximum resources
            memory: "512Mi"
            cpu: "500m"
        env:
        - name: JAVA_OPTS
          value: "-Xmx400m -XX:+UseContainerSupport"

Getting Started Commands

bash

# Install kubectl (varies by OS)
# macOS: brew install kubectl
# Linux: curl -LO "https://dl.k8s.io/release/$(curl -L -s https://dl.k8s.io/release/stable.txt)/bin/linux/amd64/kubectl"

# Start local cluster (minikube)
minikube start
kubectl config use-context minikube

# Deploy application
kubectl apply -f deployment.yaml
kubectl apply -f service.yaml

# Check status
kubectl get pods -w  # Watch pods
kubectl get services

# Access application
kubectl port-forward service/frontend-service 8080:80
# Visit http://localhost:8080

# Clean up
kubectl delete deployment,service,configmap,secret --all
minikube stop

LearnCodePro

Kubernetes — pods, deployments & services (intro)

Introduction to Kubernetes

Core Kubernetes Concepts

Pods - Smallest Deployable Units

Deployments - Managing Pod Replicas

Services - Exposing Applications

Complete Web Application Example

Frontend Deployment

Backend Deployment

Database Deployment

ConfigMaps and Secrets

ConfigMap for Configuration

Secret for Sensitive Data

Persistent Storage

Ingress for External Access

Essential kubectl Commands

Deployment Strategies

Rolling Update

Blue-Green Deployment

Monitoring and Health Checks

Namespace Organization

Resource Management

Getting Started Commands

Git workflows (feature branches, pull requests)

Docker — containers & Docker Compose for local dev

Hosting choices: Vercel, Netlify, Heroku, Render, AWS basics

CDN, Caching Headers & Static Site Best Practices

TLS/HTTPS, Domains & DNS Basics

Quick Navigation

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Topics in MERN STACK WEB DEVELOPMENT

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Introduction to Kubernetes

Core Kubernetes Concepts

Pods - Smallest Deployable Units

Deployments - Managing Pod Replicas

Services - Exposing Applications

Complete Web Application Example

Frontend Deployment

Backend Deployment

Database Deployment

ConfigMaps and Secrets

ConfigMap for Configuration

Secret for Sensitive Data

Persistent Storage

Ingress for External Access

Essential kubectl Commands

Deployment Strategies

Rolling Update

Blue-Green Deployment

Monitoring and Health Checks

Namespace Organization

Resource Management

Getting Started Commands

More in DevOps, Deployment & Scaling

Git workflows (feature branches, pull requests)

Docker — containers & Docker Compose for local dev

Hosting choices: Vercel, Netlify, Heroku, Render, AWS basics

CDN, Caching Headers & Static Site Best Practices

TLS/HTTPS, Domains & DNS Basics

Quick Navigation

This Series

Topics in MERN STACK WEB DEVELOPMENT

Categories

Learn More

Want to Track Your Progress?