kubernetes

## When to use this skill

Use this skill whenever the user wants to:
- Write Deployment, Service, ConfigMap, Secret, or Ingress manifests
- Deploy, scale, or troubleshoot pods and clusters with kubectl
- Design resource limits, health probes, rolling updates, and operational workflows
- Set up local development clusters with minikube, kind, or k3d

## How to use this skill

### Workflow

1. **Write manifests** — define workloads and services in YAML
2. **Apply to cluster** — use `kubectl apply -f` to deploy
3. **Verify status** — check rollout, pod health, and service endpoints
4. **Debug issues** — inspect logs, describe resources, exec into pods

### Quick Start Example

```yaml
# deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp
spec:
  replicas: 3
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
        - name: myapp
          image: myapp:1.0.0
          ports:
            - containerPort: 8080
          resources:
            requests:
              cpu: 100m
              memory: 128Mi
            limits:
              cpu: 500m
              memory: 256Mi
          livenessProbe:
            httpGet:
              path: /healthz
              port: 8080
            initialDelaySeconds: 10
          readinessProbe:
            httpGet:
              path: /ready
              port: 8080
---
apiVersion: v1
kind: Service
metadata:
  name: myapp
spec:
  selector:
    app: myapp
  ports:
    - port: 80
      targetPort: 8080
  type: ClusterIP
```

```bash
# Apply manifests
kubectl apply -f deployment.yaml

# Check rollout status
kubectl rollout status deployment/myapp

# View pod logs
kubectl logs -l app=myapp --tail=50

# Exec into a pod for debugging
kubectl exec -it deployment/myapp -- /bin/sh
```

### Essential kubectl Commands

| Command | Purpose |
|---------|---------|
| `kubectl apply -f <file>` | Create or update resources |
| `kubectl get pods -w` | Watch pod status |
| `kubectl describe pod <name>` | Inspect pod details and events |
| `kubectl logs <pod> -f` | Stream container logs |
| `kubectl rollout undo deployment/<name>` | Roll back a deployment |
| `kubectl scale deployment/<name> --replicas=5` | Scale replicas |

## Best Practices

- Always set `requests` and `limits` for CPU and memory
- Configure `livenessProbe` and `readinessProbe` for every container
- Use Secrets for sensitive data and ConfigMaps for configuration
- Define rolling update strategy with `maxSurge` and `maxUnavailable`
- Collect logs and metrics centrally; use RBAC and NetworkPolicies in production

## Troubleshooting

- **CrashLoopBackOff**: Run `kubectl logs <pod> --previous` to see crash output; check resource limits and probe configuration
- **ImagePullBackOff**: Verify image name/tag exists and imagePullSecrets are configured
- **Pending pods**: Run `kubectl describe pod <name>` — look for insufficient resources or unschedulable nodes
- **Service not reachable**: Verify selector labels match pod labels; check endpoints with `kubectl get endpoints <svc>`

## Keywords

kubernetes, k8s, kubectl, deployment, pod, service, ingress, configmap, secret, container orchestration