# Riferimento Rapido Kubernetes

*kubectl, pod, deployment, servizi, config, debug*

> Source: Kubernetes Documentation (kubernetes.io/docs) · MIT

## Basi kubectl

### Info Cluster

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

### Comandi Essenziali

| Command | Description |
|---------|-------------|
| `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

| Command | Description |
|---------|-------------|
| `-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

| Command | Description |
|---------|-------------|
| `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

| Command | Description |
|---------|-------------|
| `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

| Command | Description |
|---------|-------------|
| `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

| Command | Description |
|---------|-------------|
| `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

| Command | Description |
|---------|-------------|
| `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

| Command | Description |
|---------|-------------|
| `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

| Command | Description |
|---------|-------------|
| `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

| Command | Description |
|---------|-------------|
| `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 <pod> --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

| Command | Description |
|---------|-------------|
| `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` |