Basi kubectl

Info Cluster

kubectl cluster-info
kubectl get nodes
kubectl config current-context
kubectl config use-context my-cluster

Comandi Essenziali

kubectl get <resource>	Elenca risorse
kubectl describe <resource> <name>	Info dettagliate sulla risorsa
kubectl create -f file.yaml	Crea risorsa da file
kubectl apply -f file.yaml	Crea o aggiorna risorsa
kubectl delete -f file.yaml	Elimina risorsa da file
kubectl edit <resource> <name>	Modifica risorsa in-place
kubectl api-resources	Elenca tutti i tipi di risorsa

Formati di Output

-o wide	Colonne extra (IP, nodo)
-o yaml	Output YAML completo
-o json	Output JSON completo
-o jsonpath='{.spec}'	Estrae campi specifici
--sort-by=.metadata.name	Ordina output per campo

Pod

Operazioni sui Pod

kubectl get pods
kubectl get pods -A                  # all namespaces
kubectl run nginx --image=nginx      # quick pod
kubectl delete pod nginx

YAML Pod

apiVersion: v1
kind: Pod
metadata:
  name: myapp
  labels: { app: myapp }
spec:
  containers:
    - name: app
      image: nginx:1.27
      ports:
        - containerPort: 80

Valori di Stato Pod

Running	Tutti i container avviati
Pending	In attesa di scheduling o pull immagine
CrashLoopBackOff	Il container continua a crashare e riavviarsi
ImagePullBackOff	Impossibile scaricare l'immagine container
Completed	Eseguito fino al completamento (Job)

Deployment

YAML Deployment

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web
spec:
  replicas: 3
  selector:
    matchLabels: { app: web }
  template:
    metadata:
      labels: { app: web }
    spec:
      containers:
        - name: web
          image: nginx:1.27
          ports:
            - containerPort: 80

Comandi Deployment

kubectl get deploy	Elenca deployment
kubectl scale deploy web --replicas=5	Scala le repliche
kubectl set image deploy/web web=nginx:1.28	Aggiorna immagine (rolling)
kubectl rollout status deploy/web	Monitora l'avanzamento del rollout
kubectl rollout undo deploy/web	Rollback alla revisione precedente
kubectl rollout history deploy/web	Visualizza cronologia revisioni

Servizi

Tipi di Servizio

ClusterIP	Solo interno (default)
NodePort	Espone su ogni IP del nodo a porta statica
LoadBalancer	Load balancer esterno (cloud)
ExternalName	Alias DNS a servizio esterno

YAML Servizio

apiVersion: v1
kind: Service
metadata:
  name: web-svc
spec:
  type: ClusterIP
  selector: { app: web }
  ports:
    - port: 80
      targetPort: 80

Esposizione Rapida

kubectl expose deploy web --port=80 --type=ClusterIP
kubectl expose deploy web --port=80 --type=NodePort
kubectl get svc

ConfigMap e Secret

ConfigMap

kubectl create configmap app-cfg \
  --from-literal=DB_HOST=db.example.com \
  --from-file=config.ini

Secret

kubectl create secret generic db-creds \
  --from-literal=username=admin \
  --from-literal=password=s3cret

Usare nei Pod

# As environment variables
envFrom:
  - configMapRef: { name: app-cfg }
  - secretRef:    { name: db-creds }

# As volume mount
volumes:
  - name: cfg
    configMap: { name: app-cfg }

Comandi

kubectl get cm	Elenca ConfigMap
kubectl get secret	Elenca Secret
kubectl describe cm app-cfg	Mostra dati ConfigMap
kubectl get secret db-creds -o yaml	Mostra Secret (codificato base64)

Namespace

Comandi Namespace

kubectl get ns	Elenca namespace
kubectl create ns staging	Crea namespace
kubectl delete ns staging	Elimina namespace e tutte le risorse
kubectl get pods -n staging	Elenca pod nel namespace
kubectl get pods -A	Elenca pod in tutti i namespace

Imposta Namespace Default

kubectl config set-context --current \
  --namespace=staging

Volumi

PersistentVolumeClaim

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: data-pvc
spec:
  accessModes: [ReadWriteOnce]
  resources:
    requests: { storage: 10Gi }

Montare nel Pod

volumes:
  - name: data
    persistentVolumeClaim:
      claimName: data-pvc
containers:
  - volumeMounts:
      - name: data
        mountPath: /app/data

Tipi di Volume

emptyDir	Dir temporanea, eliminata con il pod
hostPath	Monta percorso del filesystem host
persistentVolumeClaim	Storage persistente (PVC)
configMap	Monta ConfigMap come file
secret	Monta Secret come file

Ingress

YAML Ingress

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: web-ingress
spec:
  rules:
    - host: app.example.com
      http:
        paths:
          - path: /
            pathType: Prefix
            backend:
              service:
                name: web-svc
                port: { number: 80 }

Note Ingress

Ingress Controller	Richiesto (nginx-ingress, traefik, ecc.)
pathType: Prefix	Corrisponde al prefisso URL
pathType: Exact	Corrisponde al percorso URL esatto
TLS	Aggiunge sezione `tls:` con nome secret

Debug

Comandi Diagnostici

kubectl logs <pod>	stdout/stderr del container
kubectl logs <pod> -c <ctr>	Log di un container specifico
kubectl logs <pod> --previous	Log dal container crashato
kubectl describe pod <pod>	Eventi, condizioni, stato
kubectl exec -it <pod> -- sh	Shell nel container
kubectl port-forward <pod> 8080:80	Inoltro porta locale al pod
kubectl top pods	Utilizzo CPU/memoria (metrics-server)
kubectl get events --sort-by=.lastTimestamp	Timeline eventi del cluster

Pod di Debug

kubectl run debug --rm -it --image=busybox -- sh
# or attach ephemeral container
kubectl debug -it  --image=busybox

Pattern Comuni

Label e Selettori

kubectl get pods -l app=web
kubectl get pods -l 'env in (prod,staging)'
kubectl label pod myapp env=prod

Limiti di Risorse

resources:
  requests: { cpu: 100m, memory: 128Mi }
  limits:   { cpu: 500m, memory: 256Mi }

Liveness e Readiness

livenessProbe:
  httpGet: { path: /healthz, port: 8080 }
  initialDelaySeconds: 5
  periodSeconds: 10
readinessProbe:
  httpGet: { path: /ready, port: 8080 }

Ricette Rapide

Dry run	`kubectl apply -f file.yaml --dry-run=client`
Genera YAML	`kubectl create deploy web --image=nginx --dry-run=client -o yaml`
Watch	`kubectl get pods -w`
Copia file	`kubectl cp file.txt pod:/tmp/`
Riavvia deploy	`kubectl rollout restart deploy/web`

RIFERIMENTO RAPIDO KUBERNETES