kubernetes-specialist

# Kubernetes Specialist

## When to Use This Skill

- Deploying workloads (Deployments, StatefulSets, DaemonSets, Jobs)
- Configuring networking (Services, Ingress, NetworkPolicies)
- Managing configuration (ConfigMaps, Secrets, environment variables)
- Setting up persistent storage (PV, PVC, StorageClasses)
- Creating Helm charts for application packaging
- Troubleshooting cluster and workload issues
- Implementing security best practices

## Core Workflow

1. **Analyze requirements** — Understand workload characteristics, scaling needs, security requirements
2. **Design architecture** — Choose workload types, networking patterns, storage solutions
3. **Implement manifests** — Create declarative YAML with proper resource limits, health checks
4. **Secure** — Apply RBAC, NetworkPolicies, Pod Security Standards, least privilege
5. **Validate** — Run `kubectl rollout status`, `kubectl get pods -w`, and `kubectl describe pod <name>` to confirm health; roll back with `kubectl rollout undo` if needed

## Reference Guide

Load detailed guidance based on context:

| Topic | Reference | Load When |
|-------|-----------|-----------|
| Workloads | `references/workloads.md` | Deployments, StatefulSets, DaemonSets, Jobs, CronJobs |
| Networking | `references/networking.md` | Services, Ingress, NetworkPolicies, DNS |
| Configuration | `references/configuration.md` | ConfigMaps, Secrets, environment variables |
| Storage | `references/storage.md` | PV, PVC, StorageClasses, CSI drivers |
| Helm Charts | `references/helm-charts.md` | Chart structure, values, templates, hooks, testing, repositories |
| Troubleshooting | `references/troubleshooting.md` | kubectl debug, logs, events, common issues |
| Custom Operators | `references/custom-operators.md` | CRD, Operator SDK, controller-runtime, reconciliation |
| Service Mesh | `references/service-mesh.md` | Istio, Linkerd, traffic management, mTLS, canary |
| GitOps | `references/gitops.md` | ArgoCD, Flux, progressive delivery, sealed secrets |
| Cost Optimization | `references/cost-optimization.md` | VPA, HPA tuning, spot instances, quotas, right-sizing |
| Multi-Cluster | `references/multi-cluster.md` | Cluster API, federation, cross-cluster networking, DR |

## Constraints

### MUST DO
- Use declarative YAML manifests (avoid imperative kubectl commands)
- Set resource requests and limits on all containers
- Include liveness and readiness probes
- Use secrets for sensitive data (never hardcode credentials)
- Apply least privilege RBAC permissions
- Implement NetworkPolicies for network segmentation
- Use namespaces for logical isolation
- Label resources consistently for organization
- Document configuration decisions in annotations

### MUST NOT DO
- Deploy to production without resource limits
- Store secrets in ConfigMaps or as plain environment variables
- Use default ServiceAccount for application pods
- Allow unrestricted network access (default allow-all)
- Run containers as root without justification
- Skip health checks (liveness/readiness probes)
- Use latest tag for production images
- Expose unnecessary ports or services

## Common YAML Patterns

### Deployment with resource limits, probes, and security context

```yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-app
  namespace: my-namespace
  labels:
    app: my-app
    version: "1.2.3"
spec:
  replicas: 3
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      labels:
        app: my-app
        version: "1.2.3"
    spec:
      serviceAccountName: my-app-sa   # never use default SA
      securityContext:
        runAsNonRoot: true
        runAsUser: 1000
        fsGroup: 2000
      containers:
        - name: my-app
          image: my-registry/my-app:1.2.3   # never use latest
          ports:
            - containerPort: 8080
          resources:
            requests:
              cpu: "100m"
              memory: "128Mi"
            limits:
              cpu: "500m"
              memory: "512Mi"
          livenessProbe:
            httpGet:
              path: /healthz
              port: 8080
            initialDelaySeconds: 15
            periodSeconds: 20
          readinessProbe:
            httpGet:
              path: /ready
              port: 8080
            initialDelaySeconds: 5
            periodSeconds: 10
          securityContext:
            allowPrivilegeEscalation: false
            readOnlyRootFilesystem: true
            capabilities:
              drop: ["ALL"]
          envFrom:
            - secretRef:
                name: my-app-secret   # pull credentials from Secret, not ConfigMap
```

### Minimal RBAC (least privilege)

```yaml
apiVersion: v1
kind: ServiceAccount
metadata:
  name: my-app-sa
  namespace: my-namespace
---
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: my-app-role
  namespace: my-namespace
rules:
  - apiGroups: [""]
    resources: ["configmaps"]
    verbs: ["get", "list"]   # grant only what is needed
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: my-app-rolebinding
  namespace: my-namespace
subjects:
  - kind: ServiceAccount
    name: my-app-sa
    namespace: my-namespace
roleRef:
  kind: Role
  name: my-app-role
  apiGroup: rbac.authorization.k8s.io
```

### NetworkPolicy (default-deny + explicit allow)

```yaml
# Deny all ingress and egress by default
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: default-deny-all
  namespace: my-namespace
spec:
  podSelector: {}
  policyTypes: ["Ingress", "Egress"]
---
# Allow only specific traffic
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-my-app
  namespace: my-namespace
spec:
  podSelector:
    matchLabels:
      app: my-app
  policyTypes: ["Ingress"]
  ingress:
    - from:
        - podSelector:
            matchLabels:
              app: frontend
      ports:
        - protocol: TCP
          port: 8080
```

## Validation Commands

After deploying, verify health and security posture:

```bash
# Watch rollout complete
kubectl rollout status deployment/my-app -n my-namespace

# Stream pod events to catch crash loops or image pull errors
kubectl get pods -n my-namespace -w

# Inspect a specific pod for failures
kubectl describe pod <pod-name> -n my-namespace

# Check container logs
kubectl logs <pod-name> -n my-namespace --previous   # use --previous for crashed containers

# Verify resource usage vs. limits
kubectl top pods -n my-namespace

# Audit RBAC permissions for a service account
kubectl auth can-i --list --as=system:serviceaccount:my-namespace:my-app-sa

# Roll back a failed deployment
kubectl rollout undo deployment/my-app -n my-namespace
```

## Output Templates

When implementing Kubernetes resources, provide:
1. Complete YAML manifests with proper structure
2. RBAC configuration if needed (ServiceAccount, Role, RoleBinding)
3. NetworkPolicy for network isolation
4. Brief explanation of design decisions and security considerations