Kubernetes Fundamentals

What is Kubernetes?

Kubernetes (K8s) is an open-source container orchestration platform that automates the deployment, scaling, and management of containerized applications. Originally developed by Google, it's now maintained by the Cloud Native Computing Foundation.

Core Concepts

Pod

The smallest deployable unit in Kubernetes. A Pod can contain one or more containers.

apiVersion: v1
kind: Pod
metadata:
  name: nginx-pod
  labels:
    app: nginx
spec:
  containers:
  - name: nginx
    image: nginx:1.20
    ports:
    - containerPort: 80

Deployment

Manages a set of replicated Pods and provides declarative updates.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.20
        ports:
        - containerPort: 80
        resources:
          requests:
            memory: "128Mi"
            cpu: "100m"
          limits:
            memory: "256Mi"
            cpu: "200m"

Service

Exposes Pods to network traffic and provides service discovery.

apiVersion: v1
kind: Service
metadata:
  name: nginx-service
spec:
  selector:
    app: nginx
  ports:
  - protocol: TCP
    port: 80
    targetPort: 80
  type: ClusterIP

Service Types

ClusterIP

Default service type, provides internal cluster access only.

apiVersion: v1
kind: Service
metadata:
  name: internal-service
spec:
  type: ClusterIP
  selector:
    app: backend
  ports:
  - port: 8080
    targetPort: 8080

NodePort

Exposes service on each node's IP at a static port.

apiVersion: v1
kind: Service
metadata:
  name: nodeport-service
spec:
  type: NodePort
  selector:
    app: web
  ports:
  - port: 80
    targetPort: 80
    nodePort: 30007

LoadBalancer

Exposes service externally using cloud provider's load balancer.

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

Ingress

Manages external access to services, typically HTTP/HTTPS.

Ingress Controller

First, you need an Ingress Controller (e.g., nginx-ingress):

kubectl apply -f https://raw.githubusercontent.com/kubernetes/ingress-nginx/controller-v1.8.1/deploy/static/provider/cloud/deploy.yaml

Ingress Resource

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: web-ingress
  annotations:
    nginx.ingress.kubernetes.io/rewrite-target: /
spec:
  ingressClassName: nginx
  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: 8080
  tls:
  - hosts:
    - myapp.example.com
    secretName: tls-secret

Configuration Management

ConfigMap

Stores non-confidential configuration data.

apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  database_url: "postgresql://db:5432/myapp"
  debug_mode: "false"
  config.properties: |
    log.level=INFO
    cache.size=100
    timeout=30

Using ConfigMap in Pod

apiVersion: v1
kind: Pod
metadata:
  name: app-pod
spec:
  containers:
  - name: app
    image: myapp:latest
    env:
    - name: DATABASE_URL
      valueFrom:
        configMapKeyRef:
          name: app-config
          key: database_url
    volumeMounts:
    - name: config-volume
      mountPath: /etc/config
  volumes:
  - name: config-volume
    configMap:
      name: app-config

Secret

Stores sensitive information like passwords, OAuth tokens, SSH keys.

apiVersion: v1
kind: Secret
metadata:
  name: db-secret
type: Opaque
data:
  username: YWRtaW4=  # base64 encoded 'admin'
  password: cGFzc3dvcmQ=  # base64 encoded 'password'

Using Secret in Pod

apiVersion: apps/v1
kind: Deployment
metadata:
  name: app-deployment
spec:
  replicas: 2
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
      - name: app
        image: myapp:latest
        env:
        - name: DB_USERNAME
          valueFrom:
            secretKeyRef:
              name: db-secret
              key: username
        - name: DB_PASSWORD
          valueFrom:
            secretKeyRef:
              name: db-secret
              key: password

Auto-scaling

Horizontal Pod Autoscaler (HPA)

apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  name: app-hpa
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: app-deployment
  minReplicas: 2
  maxReplicas: 10
  metrics:
  - type: Resource
    resource:
      name: cpu
      target:
        type: Utilization
        averageUtilization: 70
  - type: Resource
    resource:
      name: memory
      target:
        type: Utilization
        averageUtilization: 80

Vertical Pod Autoscaler (VPA)

apiVersion: autoscaling.k8s.io/v1
kind: VerticalPodAutoscaler
metadata:
  name: app-vpa
spec:
  targetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: app-deployment
  updatePolicy:
    updateMode: "Auto"
  resourcePolicy:
    containerPolicies:
    - containerName: app
      maxAllowed:
        cpu: 1000m
        memory: 2Gi
      minAllowed:
        cpu: 100m
        memory: 128Mi

Security and Access Control

RBAC (Role-Based Access Control)

Role and RoleBinding

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  namespace: development
  name: pod-reader
rules:
- apiGroups: [""]
  resources: ["pods"]
  verbs: ["get", "watch", "list"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: read-pods
  namespace: development
subjects:
- kind: User
  name: jane
  apiGroup: rbac.authorization.k8s.io
roleRef:
  kind: Role
  name: pod-reader
  apiGroup: rbac.authorization.k8s.io

ClusterRole and ClusterRoleBinding

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: cluster-admin
rules:
- apiGroups: ["*"]
  resources: ["*"]
  verbs: ["*"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: admin-binding
subjects:
- kind: User
  name: admin
  apiGroup: rbac.authorization.k8s.io
roleRef:
  kind: ClusterRole
  name: cluster-admin
  apiGroup: rbac.authorization.k8s.io

Service Account

apiVersion: v1
kind: ServiceAccount
metadata:
  name: app-service-account
  namespace: production
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: secure-app
spec:
  replicas: 3
  selector:
    matchLabels:
      app: secure-app
  template:
    metadata:
      labels:
        app: secure-app
    spec:
      serviceAccountName: app-service-account
      containers:
      - name: app
        image: myapp:latest
        securityContext:
          runAsNonRoot: true
          runAsUser: 1000
          readOnlyRootFilesystem: true

Storage

Persistent Volume and Persistent Volume Claim

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-storage
spec:
  capacity:
    storage: 10Gi
  accessModes:
  - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  storageClassName: manual
  hostPath:
    path: /data/pv-storage
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pv-claim
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 5Gi
  storageClassName: manual

Using PVC in Pod

apiVersion: apps/v1
kind: Deployment
metadata:
  name: database
spec:
  replicas: 1
  selector:
    matchLabels:
      app: database
  template:
    metadata:
      labels:
        app: database
    spec:
      containers:
      - name: postgres
        image: postgres:13
        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
        volumeMounts:
        - name: postgres-storage
          mountPath: /var/lib/postgresql/data
      volumes:
      - name: postgres-storage
        persistentVolumeClaim:
          claimName: pv-claim

Monitoring and Health Checks

Liveness and Readiness Probes

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web-app
spec:
  replicas: 3
  selector:
    matchLabels:
      app: web-app
  template:
    metadata:
      labels:
        app: web-app
    spec:
      containers:
      - name: web
        image: webapp:latest
        ports:
        - containerPort: 8080
        livenessProbe:
          httpGet:
            path: /health
            port: 8080
          initialDelaySeconds: 30
          periodSeconds: 10
          timeoutSeconds: 5
          failureThreshold: 3
        readinessProbe:
          httpGet:
            path: /ready
            port: 8080
          initialDelaySeconds: 5
          periodSeconds: 5
          timeoutSeconds: 3
          successThreshold: 1
          failureThreshold: 3
        startupProbe:
          httpGet:
            path: /startup
            port: 8080
          initialDelaySeconds: 10
          periodSeconds: 10
          timeoutSeconds: 5
          failureThreshold: 30

Essential kubectl Commands

Basic Operations

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

# Pod operations
kubectl get pods
kubectl get pods -o wide
kubectl describe pod <pod-name>
kubectl logs <pod-name>
kubectl logs <pod-name> -c <container-name>
kubectl exec -it <pod-name> -- /bin/bash

# Deployment operations
kubectl get deployments
kubectl create deployment nginx --image=nginx
kubectl scale deployment nginx --replicas=5
kubectl rollout status deployment/nginx
kubectl rollout history deployment/nginx
kubectl rollout undo deployment/nginx

# Service operations
kubectl get services
kubectl expose deployment nginx --port=80 --type=NodePort
kubectl describe service nginx

Advanced Operations

# Configuration and secrets
kubectl create configmap app-config --from-file=config.properties
kubectl create secret generic db-secret --from-literal=username=admin --from-literal=password=secret

# Resource management
kubectl top nodes
kubectl top pods
kubectl describe limitrange
kubectl describe resourcequota

# Debugging
kubectl get events --sort-by=.metadata.creationTimestamp
kubectl describe pod <pod-name>
kubectl logs <pod-name> --previous
kubectl port-forward pod/<pod-name> 8080:80

# Apply and manage manifests
kubectl apply -f deployment.yaml
kubectl delete -f deployment.yaml
kubectl get all
kubectl get all -n <namespace>

# Namespace operations
kubectl create namespace development
kubectl config set-context --current --namespace=development
kubectl get namespaces

Best Practices

Resource Management

apiVersion: apps/v1
kind: Deployment
metadata:
  name: production-app
spec:
  replicas: 3
  selector:
    matchLabels:
      app: production-app
  template:
    metadata:
      labels:
        app: production-app
    spec:
      containers:
      - name: app
        image: myapp:v1.2.3
        resources:
          requests:
            memory: "256Mi"
            cpu: "250m"
          limits:
            memory: "512Mi"
            cpu: "500m"
        securityContext:
          runAsNonRoot: true
          runAsUser: 1000
          readOnlyRootFilesystem: true
          allowPrivilegeEscalation: false
        env:
        - name: ENVIRONMENT
          value: "production"

Network Policies

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: deny-all
  namespace: production
spec:
  podSelector: {}
  policyTypes:
  - Ingress
  - Egress
---
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-frontend-to-backend
  namespace: production
spec:
  podSelector:
    matchLabels:
      tier: backend
  policyTypes:
  - Ingress
  ingress:
  - from:
    - podSelector:
        matchLabels:
          tier: frontend
    ports:
    - protocol: TCP
      port: 8080

Pod Disruption Budget

apiVersion: policy/v1
kind: PodDisruptionBudget
metadata:
  name: app-pdb
spec:
  minAvailable: 2
  selector:
    matchLabels:
      app: critical-app

Multi-Environment Configuration

Development Environment

apiVersion: v1
kind: Namespace
metadata:
  name: development
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: app
  namespace: development
spec:
  replicas: 1
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
      - name: app
        image: myapp:dev
        env:
        - name: ENVIRONMENT
          value: "development"
        - name: DEBUG
          value: "true"
        resources:
          requests:
            memory: "128Mi"
            cpu: "100m"

Production Environment

apiVersion: v1
kind: Namespace
metadata:
  name: production
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: app
  namespace: production
spec:
  replicas: 5
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
      - name: app
        image: myapp:v1.0.0
        env:
        - name: ENVIRONMENT
          value: "production"
        - name: DEBUG
          value: "false"
        resources:
          requests:
            memory: "256Mi"
            cpu: "200m"
          limits:
            memory: "512Mi"
            cpu: "500m"
        livenessProbe:
          httpGet:
            path: /health
            port: 8080
          initialDelaySeconds: 30
          periodSeconds: 10
        readinessProbe:
          httpGet:
            path: /ready
            port: 8080
          initialDelaySeconds: 5
          periodSeconds: 5

Troubleshooting

Common Issues and Solutions

# Pod stuck in Pending state
kubectl describe pod <pod-name>
kubectl get events --field-selector involvedObject.name=<pod-name>

# Pod CrashLoopBackOff
kubectl logs <pod-name> --previous
kubectl describe pod <pod-name>

# Service not accessible
kubectl get endpoints <service-name>
kubectl describe service <service-name>

# Check resource usage
kubectl top pods
kubectl describe node <node-name>

# Debug network connectivity
kubectl run test-pod --image=busybox -it --rm -- sh
# Inside pod: nslookup <service-name>

# Check RBAC permissions
kubectl auth can-i create pods --as=user@example.com
kubectl auth can-i '*' '*' --as=system:serviceaccount:default:my-sa

This comprehensive Kubernetes guide covers the fundamental concepts and practical examples needed for container orchestration in modern cloud environments.