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Kubernetes Essentials

Essential Kubernetes concepts and commands for container orchestration

March 10, 2024
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Updated regularly

Kubernetes Essentials

Quick reference guide for Kubernetes (K8s) fundamentals.

What is Kubernetes?

Kubernetes is an open-source container orchestration platform for:

  • Automated deployment of containerized applications
  • Scaling applications up and down
  • Load balancing across containers
  • Self-healing (restart failed containers)
  • Rolling updates and rollbacks
  • Service discovery and networking

    • Core Concepts

    Cluster Architecture

    Cluster
├── Control Plane (Master)
│   ├── API Server
│   ├── Scheduler
│   ├── Controller Manager
│   └── etcd (data store)
└── Worker Nodes
    ├── Kubelet (node agent)
    ├── Container Runtime (Docker/containerd)
    └── Kube-proxy (networking)

    Key Components

  • Pod: Smallest deployable unit (one or more containers)
  • Node: Worker machine (VM or physical)
  • Cluster: Set of nodes managed by Kubernetes
  • Namespace: Virtual cluster for resource isolation
  • Service: Stable endpoint for accessing pods
  • Deployment: Manages pod replicas and updates
  • ConfigMap: Configuration data
  • Secret: Sensitive data (passwords, tokens)

    • kubectl Commands

    Cluster Information

    # ========== Get Cluster Info ==========
kubectl cluster-info
kubectl version
kubectl get nodes

# ========== Node Details ==========
kubectl describe node <node-name>
kubectl top nodes          # Resource usage

# ========== Get All Resources ==========
kubectl get all
kubectl get all -A         # All namespaces

    Working with Namespaces

    # ========== List Namespaces ==========
kubectl get namespaces
kubectl get ns

# ========== Create Namespace ==========
kubectl create namespace dev
kubectl create ns prod

# ========== Use Namespace ==========
kubectl config set-context --current --namespace=dev

# ========== Delete Namespace ==========
kubectl delete namespace dev

    Pods

    # ========== List Pods ==========
kubectl get pods
kubectl get pods -o wide        # More details
kubectl get pods -A             # All namespaces
kubectl get pods -w             # Watch for changes

# ========== Create Pod (from YAML) ==========
kubectl apply -f pod.yaml

# ========== Get Pod Details ==========
kubectl describe pod <pod-name>

# ========== View Logs ==========
kubectl logs <pod-name>
kubectl logs <pod-name> -f      # Follow logs
kubectl logs <pod-name> -c <container-name>  # Specific container

# ========== Execute Command in Pod ==========
kubectl exec <pod-name> -- <command>
kubectl exec -it <pod-name> -- /bin/bash     # Interactive shell

# ========== Delete Pod ==========
kubectl delete pod <pod-name>
kubectl delete pod <pod-name> --force --grace-period=0  # Force delete

    Deployments

    # ========== List Deployments ==========
kubectl get deployments
kubectl get deploy

# ========== Create Deployment ==========
kubectl create deployment nginx --image=nginx:latest

# ========== Create from YAML ==========
kubectl apply -f deployment.yaml

# ========== Scale Deployment ==========
kubectl scale deployment <name> --replicas=5

# ========== Update Image ==========
kubectl set image deployment/<name> <container>=<new-image>

# ========== Rollout Status ==========
kubectl rollout status deployment/<name>
kubectl rollout history deployment/<name>

# ========== Rollback ==========
kubectl rollout undo deployment/<name>
kubectl rollout undo deployment/<name> --to-revision=2

# ========== Delete Deployment ==========
kubectl delete deployment <name>

    Services

    # ========== List Services ==========
kubectl get services
kubectl get svc

# ========== Expose Deployment ==========
kubectl expose deployment <name> --port=80 --type=LoadBalancer

# ========== Get Service Details ==========
kubectl describe service <name>

# ========== Delete Service ==========
kubectl delete service <name>

    ConfigMaps and Secrets

    # ========== ConfigMaps ==========
kubectl create configmap app-config --from-literal=key=value
kubectl create configmap app-config --from-file=config.properties
kubectl get configmaps
kubectl describe configmap app-config
kubectl delete configmap app-config

# ========== Secrets ==========
kubectl create secret generic db-secret --from-literal=password=secret123
kubectl create secret docker-registry regcred --docker-server=<server> --docker-username=<user> --docker-password=<pass>
kubectl get secrets
kubectl describe secret db-secret
kubectl delete secret db-secret

    YAML Manifests

    Pod Definition

    apiVersion: v1
kind: Pod
metadata:
  name: nginx-pod
  labels:
    app: nginx
spec:
  containers:
  - name: nginx
    image: nginx:latest
    ports:
    - containerPort: 80
    env:
    - name: ENVIRONMENT
      value: "production"
    resources:
      requests:
        memory: "64Mi"
        cpu: "250m"
      limits:
        memory: "128Mi"
        cpu: "500m"

    Deployment Definition

    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:latest
        ports:
        - containerPort: 80
        livenessProbe:
          httpGet:
            path: /
            port: 80
          initialDelaySeconds: 30
          periodSeconds: 10
        readinessProbe:
          httpGet:
            path: /
            port: 80
          initialDelaySeconds: 5
          periodSeconds: 5

    Service Definition

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

---
# ========== NodePort (External Access) ==========
apiVersion: v1
kind: Service
metadata:
  name: nginx-nodeport
spec:
  selector:
    app: nginx
  type: NodePort
  ports:
  - port: 80
    targetPort: 80
    nodePort: 30080

---
# ========== LoadBalancer ==========
apiVersion: v1
kind: Service
metadata:
  name: nginx-lb
spec:
  selector:
    app: nginx
  type: LoadBalancer
  ports:
  - port: 80
    targetPort: 80

    ConfigMap Definition

    apiVersion: v1
kind: ConfigMap
metadata:
  name: app-config
data:
  database_url: "postgres://db:5432"
  log_level: "info"
  config.properties: |
    property1=value1
    property2=value2

    Secret Definition

    apiVersion: v1
kind: Secret
metadata:
  name: db-secret
type: Opaque
data:
  username: YWRtaW4=         # base64 encoded "admin"
  password: cGFzc3dvcmQxMjM=  # base64 encoded "password123"

    Using ConfigMap and Secret in Pod

    apiVersion: v1
kind: Pod
metadata:
  name: app-pod
spec:
  containers:
  - name: app
    image: myapp:latest
    env:
    # Environment variable from ConfigMap
    - name: DATABASE_URL
      valueFrom:
        configMapKeyRef:
          name: app-config
          key: database_url
    # Environment variable from Secret
    - name: DB_PASSWORD
      valueFrom:
        secretKeyRef:
          name: db-secret
          key: password
    # Mount ConfigMap as volume
    volumeMounts:
    - name: config-volume
      mountPath: /etc/config
  volumes:
  - name: config-volume
    configMap:
      name: app-config

    Ingress

    Route external traffic to services:

    apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: app-ingress
  annotations:
    nginx.ingress.kubernetes.io/rewrite-target: /
spec:
  ingressClassName: nginx
  rules:
  - host: myapp.example.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: app-service
            port:
              number: 80
      - path: /api
        pathType: Prefix
        backend:
          service:
            name: api-service
            port:
              number: 8080
  tls:
  - hosts:
    - myapp.example.com
    secretName: tls-secret

    Persistent Volumes

    Store data persistently:

    PersistentVolume (PV)

    apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-storage
spec:
  capacity:
    storage: 10Gi
  accessModes:
  - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  storageClassName: standard
  hostPath:
    path: /data

    PersistentVolumeClaim (PVC)

    apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc-storage
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 5Gi
  storageClassName: standard

    Using PVC in Pod

    apiVersion: v1
kind: Pod
metadata:
  name: app-with-storage
spec:
  containers:
  - name: app
    image: myapp:latest
    volumeMounts:
    - name: data
      mountPath: /app/data
  volumes:
  - name: data
    persistentVolumeClaim:
      claimName: pvc-storage

    StatefulSet

    For stateful applications (databases, etc.):

    apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: mongodb
spec:
  serviceName: mongodb-service
  replicas: 3
  selector:
    matchLabels:
      app: mongodb
  template:
    metadata:
      labels:
        app: mongodb
    spec:
      containers:
      - name: mongodb
        image: mongo:latest
        ports:
        - containerPort: 27017
        volumeMounts:
        - name: data
          mountPath: /data/db
  volumeClaimTemplates:
  - metadata:
      name: data
    spec:
      accessModes: ["ReadWriteOnce"]
      resources:
        requests:
          storage: 10Gi

    Jobs and CronJobs

    Job (Run Once)

    apiVersion: batch/v1
kind: Job
metadata:
  name: data-migration
spec:
  template:
    spec:
      containers:
      - name: migration
        image: migration-image:latest
        command: ["./migrate"]
      restartPolicy: OnFailure
  backoffLimit: 3

    CronJob (Scheduled)

    apiVersion: batch/v1
kind: CronJob
metadata:
  name: backup-job
spec:
  schedule: "0 2 * * *"  # Every day at 2 AM
  jobTemplate:
    spec:
      template:
        spec:
          containers:
          - name: backup
            image: backup-image:latest
            command: ["./backup.sh"]
          restartPolicy: OnFailure

    Resource Management

    Resource Requests and Limits

    apiVersion: v1
kind: Pod
metadata:
  name: resource-demo
spec:
  containers:
  - name: app
    image: myapp:latest
    resources:
      requests:
        memory: "256Mi"    # Minimum guaranteed
        cpu: "500m"        # 0.5 CPU cores
      limits:
        memory: "512Mi"    # Maximum allowed
        cpu: "1000m"       # 1 CPU core

    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

    Health Checks

    Liveness and Readiness Probes

    apiVersion: v1
kind: Pod
metadata:
  name: health-check-demo
spec:
  containers:
  - name: app
    image: myapp:latest
    ports:
    - containerPort: 8080
    
    # Liveness: Restart if fails
    livenessProbe:
      httpGet:
        path: /healthz
        port: 8080
      initialDelaySeconds: 30
      periodSeconds: 10
      timeoutSeconds: 5
      failureThreshold: 3
    
    # Readiness: Remove from service if fails
    readinessProbe:
      httpGet:
        path: /ready
        port: 8080
      initialDelaySeconds: 5
      periodSeconds: 5
      timeoutSeconds: 3
      failureThreshold: 2
    
    # Startup: Check on container start
    startupProbe:
      httpGet:
        path: /startup
        port: 8080
      initialDelaySeconds: 0
      periodSeconds: 10
      failureThreshold: 30

    Debugging

    Common Debugging Commands

    # ========== Check Pod Status ==========
kubectl get pods
kubectl describe pod <pod-name>

# ========== View Logs ==========
kubectl logs <pod-name>
kubectl logs <pod-name> --previous        # Previous container logs

# ========== Get Events ==========
kubectl get events --sort-by=.metadata.creationTimestamp
kubectl get events -n <namespace>

# ========== Exec into Container ==========
kubectl exec -it <pod-name> -- /bin/bash
kubectl exec -it <pod-name> -- sh

# ========== Port Forward ==========
kubectl port-forward <pod-name> 8080:80
kubectl port-forward service/<service-name> 8080:80

# ========== Debug with Ephemeral Container ==========
kubectl debug <pod-name> -it --image=busybox

# ========== Check Resource Usage ==========
kubectl top pods
kubectl top nodes

# ========== Describe Resources ==========
kubectl describe deployment <name>
kubectl describe service <name>
kubectl describe node <name>

    Common Issues

    # ========== ImagePullBackOff ==========
# Check image name, registry credentials
kubectl describe pod <pod-name>

# ========== CrashLoopBackOff ==========
# Check logs for errors
kubectl logs <pod-name>
kubectl logs <pod-name> --previous

# ========== Pending Pods ==========
# Check node resources, scheduling constraints
kubectl describe pod <pod-name>
kubectl get nodes
kubectl top nodes

    Best Practices

    Labels and Selectors

    metadata:
  labels:
    app: myapp
    version: v1.0.0
    environment: production
    team: backend

    Resource Quotas

    apiVersion: v1
kind: ResourceQuota
metadata:
  name: dev-quota
  namespace: dev
spec:
  hard:
    requests.cpu: "10"
    requests.memory: 20Gi
    limits.cpu: "20"
    limits.memory: 40Gi
    pods: "20"

    Network Policies

    apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-frontend
spec:
  podSelector:
    matchLabels:
      app: backend
  policyTypes:
  - Ingress
  ingress:
  - from:
    - podSelector:
        matchLabels:
          app: frontend
    ports:
    - protocol: TCP
      port: 8080

    Helm (Package Manager)

    Basic Commands

    # ========== Add Repository ==========
helm repo add stable https://charts.helm.sh/stable
helm repo update

# ========== Search Charts ==========
helm search repo nginx

# ========== Install Chart ==========
helm install myapp stable/nginx
helm install myapp ./mychart -f values.yaml

# ========== List Releases ==========
helm list
helm list -A

# ========== Upgrade Release ==========
helm upgrade myapp stable/nginx
helm upgrade myapp ./mychart --set image.tag=v2.0

# ========== Rollback ==========
helm rollback myapp 1

# ========== Uninstall ==========
helm uninstall myapp

    Tips

  • Use namespaces to organize resources
  • Set resource limits to prevent resource exhaustion
  • Use health checks for reliability
  • Label everything for better organization
  • Use ConfigMaps/Secrets for configuration
  • Monitor logs and metrics regularly
  • Use Helm for complex deployments
  • Version control all YAML files
  • Test in dev before deploying to production
  • Implement autoscaling for variable loads

    • Common Patterns

    Blue-Green Deployment

    # Blue (current version)
apiVersion: apps/v1
kind: Deployment
metadata:
  name: app-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

---
# Service points to blue
apiVersion: v1
kind: Service
metadata:
  name: app-service
spec:
  selector:
    app: myapp
    version: blue  # Switch to green when ready
  ports:
  - port: 80

    Sidecar Pattern

    apiVersion: v1
kind: Pod
metadata:
  name: app-with-sidecar
spec:
  containers:
  # Main application
  - name: app
    image: myapp:latest
    ports:
    - containerPort: 8080
  # Sidecar (logging agent)
  - name: log-agent
    image: fluentd:latest
    volumeMounts:
    - name: logs
      mountPath: /var/log
  volumes:
  - name: logs
    emptyDir: {}

    Resources

  • Kubernetes Official Documentation
  • kubectl Cheat Sheet
  • Kubernetes By Example
  • Helm Documentation
  • Kubernetes Patterns

    • Topics

    KubernetesDevOpsDockerContainerCloud
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