kubernetes-basics

## Purpose Orchestrate containerized applications across clusters of machines with automated deployment, scaling, and management. ## When to Use - Deploying containerized applications - Managing microservices - Scaling applications - Implementing CI/CD pipelines - Managing multi-container applications ## Core Concepts ### Pod Smallest deployable unit. Contains one or more containers sharing storage/network. ```yaml apiVersion: v1 kind: Pod metadata: name: my-pod spec: containers: - name: my-container image: nginx:1.25 ports: - containerPort: 80 ``` ### Deployment Manages Pod replicas and updates. ```yaml apiVersion: apps/v1 kind: Deployment metadata: name: my-deployment spec: replicas: 3 selector: matchLabels: app: myapp template: metadata: labels: app: myapp spec: containers: - name: my-container image: nginx:1.25 ports: - containerPort: 80 ``` ### Service Exposes Pods as network service. ```yaml apiVersion: v1 kind: Service metadata: name: my-service spec: selector: app: myapp ports: - port: 80 targetPort: 80 type: LoadBalancer ``` ### ConfigMap Stores configuration data. ```yaml apiVersion: v1 kind: ConfigMap metadata: name: my-config data: database.url: "postgres://localhost:5432/mydb" cache.ttl: "3600" ``` ### Secret Stores sensitive data (base64 encoded). ```yaml apiVersion: v1 kind: Secret metadata: name: my-secret type: Opaque data: password: cGFzc3dvcmQ= # base64 encoded "password" ``` ## Installation ### Minikube (Local Development) ```bash # Install curl -LO https://storage.googleapis.com/minikube/releases/latest/minikube-linux-amd64 sudo install minikube-linux-amd64 /usr/local/bin/minikube # Start minikube start # Stop minikube stop ``` ### Kind (Local Development) ```bash # Install go install sigs.k8s.io/kind@latest # Create cluster kind create cluster # Delete cluster kind delete cluster ``` ### k3s (Lightweight) ```bash # Install curl -sfL https://get.k3s.io | sh - # Check status sudo k3s kubectl get nodes ``` ### Cloud Providers - **GKE**: Google Kubernetes Engine - **EKS**: Amazon Elastic Kubernetes Service - **AKS**: Azure Kubernetes Service ## kubectl Commands ### Cluster Info ```bash # Get cluster info kubectl cluster-info # Get nodes kubectl get nodes # Get namespaces kubectl get namespaces ``` ### Pods ```bash # List pods kubectl get pods # Describe pod kubectl describe pod <pod-name> # Get pod logs kubectl logs <pod-name> # Exec into pod kubectl exec -it <pod-name> -- sh # Delete pod kubectl delete pod <pod-name> ``` ### Deployments ```bash # Create deployment kubectl create deployment myapp --image=nginx # Scale deployment kubectl scale deployment myapp --replicas=3 # Update image kubectl set image deployment/myapp nginx=nginx:1.26 # Rollback kubectl rollout undo deployment/myapp # Check rollout status kubectl rollout status deployment/myapp ``` ### Services ```bash # List services kubectl get services # Expose deployment kubectl expose deployment myapp --port=80 --type=LoadBalancer # Delete service kubectl delete service myapp ``` ### Apply/Delete ```bash # Apply from file kubectl apply -f deployment.yaml # Apply from directory kubectl apply -f k8s/ # Delete from file kubectl delete -f deployment.yaml ``` ## Common Configurations ### Node.js Application ```yaml apiVersion: apps/v1 kind: Deployment metadata: name: nodejs-app spec: replicas: 3 selector: matchLabels: app: nodejs template: metadata: labels: app: nodejs spec: containers: - name: nodejs image: node:20-alpine command: ["node", "index.js"] ports: - containerPort: 3000 env: - name: PORT value: "3000" - name: NODE_ENV value: "production" resources: requests: memory: "128Mi" cpu: "100m" limits: memory: "256Mi" cpu: "200m" --- apiVersion: v1 kind: Service metadata: name: nodejs-service spec: selector: app: nodejs ports: - port: 80 targetPort: 3000 type: LoadBalancer ``` ### PostgreSQL Database ```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-alpine ports: - containerPort: 5432 env: - name: POSTGRES_PASSWORD valueFrom: secretKeyRef: name: postgres-secret key: password volumeMounts: - name: postgres-storage mountPath: /var/lib/postgresql/data volumes: - name: postgres-storage persistentVolumeClaim: claimName: postgres-pvc --- apiVersion: v1 kind: PersistentVolumeClaim metadata: name: postgres-pvc spec: accessModes: - ReadWriteOnce resources: requests: storage: 10Gi --- apiVersion: v1 kind: Service metadata: name: postgres-service spec: selector: app: postgres ports: - port: 5432 targetPort: 5432 type: ClusterIP ``` ### Redis Cache ```yaml apiVersion: apps/v1 kind: Deployment metadata: name: redis spec: replicas: 1 selector: matchLabels: app: redis template: metadata: labels: app: redis spec: containers: - name: redis image: redis:7-alpine ports: - containerPort: 6379 resources: requests: memory: "64Mi" cpu: "50m" limits: memory: "128Mi" cpu: "100m" --- apiVersion: v1 kind: Service metadata: name: redis-service spec: selector: app: redis ports: - port: 6379 targetPort: 6379 type: ClusterIP ``` ## Latest Kubernetes Features (2024-2026) ### v1.32 (Penelope) - December 2024 - Dynamic resource allocation for pods (beta) - AppArmor support (stable) - CEL for admission control (beta) - Improved pod disruption budgets ### v1.33 - 2025 - Job resource modification in suspended jobs (beta) - Enhanced network policies - Improved CSI volume support - Better resource metrics ### v1.34 - 2025 - Gateway API (beta) - Improved pod scheduling - Enhanced security contexts - Better observability features ### v1.35 - 2025 - Container resource modification in suspended jobs (alpha → beta) - Queue controller improvements - Network policy enhancements - Storage improvements ### v1.36 - 2025/2026 - Gateway API improvements - Enhanced job management - Better multi-cluster support - Improved security features ## Deployment Strategies ### Rolling Update (Default) Gradually replaces old pods with new ones. ```yaml spec: strategy: type: RollingUpdate rollingUpdate: maxSurge: 25% maxUnavailable: 25% ``` ### Recreate Shuts down all pods before starting new ones. ```yaml spec: strategy: type: Recreate ``` ### Blue/Green Maintains two versions, switches traffic instantly. ```yaml # Create two deployments apiVersion: apps/v1 kind: Deployment metadata: name: myapp-blue spec: # ... blue configuration --- apiVersion: apps/v1 kind: Deployment metadata: name: myapp-green spec: # ... green configuration ``` ### Canary Deploys new version to subset of users. ```yaml apiVersion: flagger.app/v1beta1 kind: Canary metadata: name: myapp spec: targetRef: apiVersion: apps/v1 kind: Deployment name: myapp service: port: 80 analysis: interval: 1m threshold: 5 maxWeight: 50 ``` ## Ingress ### NGINX Ingress Controller ```yaml apiVersion: networking.k8s.io/v1 kind: Ingress metadata: name: my-ingress annotations: nginx.ingress.kubernetes.io/rewrite-target: / spec: rules: - host: myapp.example.com http: paths: - path: / pathType: Prefix backend: service: name: my-service port: number: 80 ``` ## Horizontal Pod Autoscaler ```yaml apiVersion: autoscaling/v2 kind: HorizontalPodAutoscaler metadata: name: myapp-hpa spec: scaleTargetRef: apiVersion: apps/v1 kind: Deployment name: myapp minReplicas: 2 maxReplicas: 10 metrics: - type: Resource resource: name: cpu target: type: Utilization averageUtilization: 80 ``` ## Namespaces ### Create Namespace ```yaml apiVersion: v1 kind: Namespace metadata: name: development ``` ### Set Default Namespace ```bash kubectl config set-context --current --namespace=development ``` ## Resource Limits ### Pod Resources ```yaml spec: containers: - name: my-container image: nginx resources: requests: memory: "64Mi" cpu: "250m" limits: memory: "128Mi" cpu: "500m" ``` ## Health Checks ### Liveness Probe ```yaml spec: containers: - name: my-container livenessProbe: httpGet: path: /health port: 8080 initialDelaySeconds: 30 periodSeconds: 10 ``` ### Readiness Probe ```yaml spec: containers: - name: my-container readinessProbe: httpGet: path: /ready port: 8080 initialDelaySeconds: 5 periodSeconds: 5 ``` ## Best Practices ### Image Management - Use specific image tags (not `latest`) - Scan images for vulnerabilities - Use multi-stage builds - Keep images small ### Resource Management - Set resource requests and limits - Use Horizontal Pod Autoscaler - Monitor resource usage - Right-size your pods ### Security - Use non-root containers - Scan images for vulnerabilities - Use secrets for sensitive data - Enable network policies - Use RBAC for access control ### Configuration - Use ConfigMaps for config - Use Secrets for sensitive data - Externalize configuration - Use environment variables ### High Availability - Use multiple replicas - Use anti-affinity rules - Distribute across nodes - Use persistent storage for stateful apps ## Common Issues ### Pod Not Starting ```bash # Check pod status kubectl describe pod <pod-name> # Check logs kubectl logs <pod-name> # Check events kubectl get events ``` ### Image Pull Errors ```bash # Check image pull secrets kubectl get secrets # Create image pull secret kubectl create secret docker-registry regcred \ --docker-server=<registry> \ --docker-username=<user> \ --docker-password=<pass> ``` ### Resource Exhaustion ```bash # Check node resources kubectl top nodes # Check pod resources kubectl top pods # Describe node kubectl describe node <node-name> ``` ## Tools ### kubectl Main CLI tool for Kubernetes. ### k9s Terminal UI for Kubernetes. ```bash brew install k9s ``` ### Lens GUI for Kubernetes management. ### Helm Package manager for Kubernetes. ```bash # Install brew install helm # Add repo helm repo add stable https://charts.helm.sh/stable # Install chart helm install my-release stable/nginx ``` ### ArgoCD GitOps continuous delivery for Kubernetes. ## Monitoring ### Prometheus + Grafana ```yaml apiVersion: v1 kind: ConfigMap metadata: name: prometheus-config data: prometheus.yml: | global: scrape_interval: 15s scrape_configs: - job_name: 'kubernetes-pods' kubernetes_sd_configs: - role: pod ``` ## Troubleshooting ### Debug Pods ```bash # Check pod status kubectl get pods # Describe pod kubectl describe pod <pod-name> # View logs kubectl logs <pod-name> # Exec into pod kubectl exec -it <pod-name> -- sh ``` ### Debug Services ```bash # Check service endpoints kubectl get endpoints <service-name> # Test service from pod kubectl run -it --rm debug --image=nicolaka/netshoot --restart=Never -- sh ``` ### Debug Network ```bash # Check network policies kubectl get networkpolicies # Check DNS kubectl run -it --rm debug --image=busybox --restart=Never -- nslookup kubernetes.default ``` ## Scripts ### deploy.sh ```bash #!/bin/bash kubectl apply -f k8s/ kubectl rollout status deployment/myapp ``` ### scale.sh ```bash #!/bin/bash kubectl scale deployment myapp --replicas=$1 ``` ### logs.sh ```bash