Kubernetes (K8s)¶

# Cluster info
kubectl cluster-info                # Show cluster endpoints
kubectl version                     # Client and server version
kubectl get nodes                   # List cluster nodes

# Resource management (pods, deployments, services)
kubectl get pods                    # List pods in current namespace
kubectl get pods -A                 # List pods in all namespaces
kubectl get deployments             # List deployments
kubectl get services                # List services
kubectl get all                     # Everything in namespace

# Detailed resource info
kubectl describe pod pod-name       # Detailed pod information
kubectl describe node node-name     # Node details (capacity, conditions)
kubectl logs pod-name               # Pod logs
kubectl logs -f pod-name            # Follow logs (like tail -f)
kubectl logs pod-name -c container  # Logs from specific container (multi-container pods)

# Execution and debugging
kubectl exec -it pod-name -- bash   # Interactive shell in pod
kubectl exec pod-name -- ls /app    # Run command in pod
kubectl port-forward pod-name 8080:80  # Forward local port to pod

# Apply and manage resources
kubectl apply -f deployment.yaml    # Create/update resources
kubectl delete -f deployment.yaml   # Delete resources
kubectl delete pod pod-name         # Delete specific pod
kubectl scale deployment app --replicas=3  # Scale deployment

# Rollouts (deployments)
kubectl rollout status deployment/app   # Check rollout status
kubectl rollout history deployment/app  # View rollout history
kubectl rollout undo deployment/app     # Rollback to previous version
kubectl rollout restart deployment/app  # Restart all pods

# Namespace management
kubectl get namespaces              # List namespaces
kubectl config set-context --current --namespace=dev  # Switch namespace
kubectl create namespace staging    # Create namespace

# Context management (multiple clusters)
kubectl config get-contexts         # List available contexts
kubectl config use-context prod     # Switch to prod cluster
kubectl config current-context      # Show current context

# deployment.yaml - The bread and butter of K8s
apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-app
  namespace: production
  labels:
    app: web
    tier: frontend
spec:
  replicas: 3  # (1)!
  selector:
    matchLabels:
      app: web
  strategy:
    type: RollingUpdate  # (2)!
    rollingUpdate:
      maxUnavailable: 1
      maxSurge: 1
  template:
    metadata:
      labels:
        app: web
        tier: frontend
    spec:
      containers:
      - name: web
        image: myregistry/web-app:1.2.3  # (3)!
        imagePullPolicy: IfNotPresent
        ports:
        - containerPort: 8080
          name: http
        env:
        - name: DATABASE_URL
          valueFrom:
            secretKeyRef:  # (4)!
              name: db-credentials
              key: url
        - name: LOG_LEVEL
          valueFrom:
            configMapKeyRef:  # (5)!
              name: app-config
              key: log_level
        resources:  # (6)!
          requests:
            memory: "256Mi"
            cpu: "250m"
          limits:
            memory: "512Mi"
            cpu: "500m"
        livenessProbe:  # (7)!
          httpGet:
            path: /health
            port: 8080
          initialDelaySeconds: 30
          periodSeconds: 10
        readinessProbe:  # (8)!
          httpGet:
            path: /ready
            port: 8080
          initialDelaySeconds: 5
          periodSeconds: 5
      imagePullSecrets:  # (9)!
      - name: registry-credentials

# service.yaml - Expose deployment with stable IP/DNS
apiVersion: v1
kind: Service
metadata:
  name: web-service
  namespace: production
spec:
  type: ClusterIP  # (1)!
  selector:
    app: web  # Matches pods with this label
  ports:
  - port: 80        # Service port
    targetPort: 8080  # Container port
    protocol: TCP
    name: http
  sessionAffinity: ClientIP  # (2)!
---
apiVersion: v1
kind: Service
metadata:
  name: web-external
  namespace: production
spec:
  type: LoadBalancer  # (3)!
  selector:
    app: web
  ports:
  - port: 80
    targetPort: 8080

# ingress.yaml - HTTP routing with SSL/TLS
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: web-ingress
  namespace: production
  annotations:
    cert-manager.io/cluster-issuer: letsencrypt-prod  # (1)!
    nginx.ingress.kubernetes.io/ssl-redirect: "true"
    nginx.ingress.kubernetes.io/rate-limit: "100"  # (2)!
spec:
  ingressClassName: nginx  # (3)!
  tls:
  - hosts:
    - myapp.example.com
    secretName: myapp-tls  # (4)!
  rules:
  - host: myapp.example.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: web-service
            port:
              number: 80
      - path: /api
        pathType: Prefix
        backend:
          service:
            name: api-service
            port:
              number: 8080