Kubernetes

Kubernetes

Essential kubectl commands and Kubernetes patterns.

Context & Namespace

# View contexts
kubectl config get-contexts
kubectl config current-context

# Switch context
kubectl config use-context production

# Set default namespace
kubectl config set-context --current --namespace=my-app

# Use namespace in command
kubectl get pods -n kube-system
kubectl get pods --all-namespaces  # or -A

Pods

# List pods
kubectl get pods
kubectl get pods -o wide              # More details
kubectl get pods -w                    # Watch mode
kubectl get pods --show-labels
kubectl get pods -l app=web            # By label

# Pod details
kubectl describe pod my-pod
kubectl get pod my-pod -o yaml

# Logs
kubectl logs my-pod
kubectl logs my-pod -f                 # Follow
kubectl logs my-pod --tail=100
kubectl logs my-pod -c my-container    # Specific container
kubectl logs my-pod --previous         # Previous crash

# Exec into pod
kubectl exec -it my-pod -- /bin/sh
kubectl exec -it my-pod -c my-container -- bash

# Port forward
kubectl port-forward my-pod 8080:80
kubectl port-forward svc/my-service 8080:80

# Copy files
kubectl cp my-pod:/app/file.txt ./file.txt
kubectl cp ./file.txt my-pod:/app/

# Delete
kubectl delete pod my-pod
kubectl delete pod my-pod --grace-period=0 --force

Deployments

# Create deployment
kubectl create deployment web --image=nginx:latest --replicas=3

# List
kubectl get deployments
kubectl get deploy

# Scale
kubectl scale deployment web --replicas=5

# Update image
kubectl set image deployment/web nginx=nginx:1.25

# Rollout status
kubectl rollout status deployment/web

# Rollback
kubectl rollout undo deployment/web
kubectl rollout undo deployment/web --to-revision=2

# History
kubectl rollout history deployment/web

# Restart (rolling)
kubectl rollout restart deployment/web

Deployment YAML

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web
  labels:
    app: web
spec:
  replicas: 3
  selector:
    matchLabels:
      app: web
  template:
    metadata:
      labels:
        app: web
    spec:
      containers:
        - name: web
          image: nginx:1.25
          ports:
            - containerPort: 80
          resources:
            requests:
              cpu: 100m
              memory: 128Mi
            limits:
              cpu: 500m
              memory: 256Mi
          livenessProbe:
            httpGet:
              path: /health
              port: 80
            initialDelaySeconds: 10
            periodSeconds: 30
          readinessProbe:
            httpGet:
              path: /ready
              port: 80
            initialDelaySeconds: 5
            periodSeconds: 10
          env:
            - name: NODE_ENV
              value: "production"
            - name: DB_PASSWORD
              valueFrom:
                secretKeyRef:
                  name: db-secret
                  key: password

Services

# ClusterIP (internal)
apiVersion: v1
kind: Service
metadata:
  name: web
spec:
  selector:
    app: web
  ports:
    - port: 80
      targetPort: 8080

---
# LoadBalancer (external)
apiVersion: v1
kind: Service
metadata:
  name: web-public
spec:
  type: LoadBalancer
  selector:
    app: web
  ports:
    - port: 80
      targetPort: 8080

---
# NodePort
apiVersion: v1
kind: Service
metadata:
  name: web-nodeport
spec:
  type: NodePort
  selector:
    app: web
  ports:
    - port: 80
      targetPort: 8080
      nodePort: 30080

# Quick expose
kubectl expose deployment web --port=80 --target-port=8080
kubectl expose deployment web --type=LoadBalancer --port=80

# List services
kubectl get svc
kubectl describe svc web

ConfigMaps & Secrets

# ConfigMap
kubectl create configmap app-config --from-literal=key=value
kubectl create configmap app-config --from-file=config.yaml

# Secret
kubectl create secret generic db-creds \
  --from-literal=username=admin \
  --from-literal=password=secret123

# View
kubectl get configmap app-config -o yaml
kubectl get secret db-creds -o jsonpath='{.data.password}' | base64 -d

Apply & Delete

# Apply manifest
kubectl apply -f deployment.yaml
kubectl apply -f ./k8s/              # All files in directory
kubectl apply -f https://example.com/manifest.yaml

# Delete
kubectl delete -f deployment.yaml
kubectl delete deployment web
kubectl delete all -l app=web        # By label

# Dry run
kubectl apply -f deployment.yaml --dry-run=client
kubectl apply -f deployment.yaml --dry-run=server

Debugging Quick Reference

# Pod not starting?
kubectl describe pod my-pod          # Check Events section
kubectl get events --sort-by='.lastTimestamp'

# CrashLoopBackOff?
kubectl logs my-pod --previous       # Logs from crashed container

# Can't connect to service?
kubectl get endpoints my-service     # Check if endpoints exist
kubectl run debug --rm -it --image=busybox -- wget -qO- http://my-service

# Resource issues?
kubectl top pods
kubectl top nodes
kubectl describe node <node-name>    # Check Allocatable vs Allocated

Reference

For debugging patterns: references/debugging.md For YAML templates: references/manifests.md