Kubernetes Hardening

Secure Kubernetes clusters and workloads.

When to Use This Skill

Use this skill when:

• Hardening Kubernetes clusters
• Implementing Pod Security Standards
• Configuring network policies
• Meeting security compliance

Scope and validation

Confirm the exact cluster/namespace/version and authorized writes before applying policies. Examples are fragments: validate the reviewed image, namespace, service accounts, labels and required runtime storage. Pin the policy version to the target Kubernetes release where supported. Restricted admission controls new/updated pods; it does not retroactively fix running workloads or establish compliance.

Pod Security Standards

# Namespace with restricted policy
apiVersion: v1
kind: Namespace
metadata:
  name: production
  labels:
    pod-security.kubernetes.io/enforce: restricted
    pod-security.kubernetes.io/audit: restricted
    pod-security.kubernetes.io/warn: restricted

Security Context

apiVersion: v1
kind: Pod
metadata:
  name: secure-pod
  labels:
    app: web
spec:
  securityContext:
    runAsNonRoot: true
    runAsUser: 1000
    runAsGroup: 1000
    fsGroup: 1000
    seccompProfile:
      type: RuntimeDefault
  containers:
  - name: app
    image: registry.example.invalid/myapp:REVIEWED_IMMUTABLE_TAG
    securityContext:
      allowPrivilegeEscalation: false
      readOnlyRootFilesystem: true
      capabilities:
        drop: ["ALL"]

Network Policies

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: default-deny-all
spec:
  podSelector: {}
  policyTypes:
  - Ingress
  - Egress
---
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-web
spec:
  podSelector:
    matchLabels:
      app: web
  ingress:
  - from:
    - podSelector:
        matchLabels:
          app: frontend
    ports:
    - port: 8080

RBAC

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: app-reader
rules:
- apiGroups: [""]
  resources: ["pods", "services"]
  verbs: ["get", "list"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: app-reader-binding
subjects:
- kind: ServiceAccount
  name: myapp
roleRef:
  kind: Role
  name: app-reader
  apiGroup: rbac.authorization.k8s.io

Best Practices

• Enable Pod Security Standards
• Implement network policies
• Use RBAC with least privilege
• Enable audit logging
• Secure etcd with encryption
• Use service mesh for mTLS
• Regular security scanning

Related Skills

• kubernetes-ops (kubernetes-ops) - K8s operations
• container-hardening (container-hardening) - Container security

Limitations

• Apply guidance only within authorized scope; test destructive steps in non-production first.
• Docs-only import: upstream scripts and templates not bundled.

Example

# Read-only first: inventory before any active step.
which <tool> && <tool> --help | head -n 20

Adapted from BagelHole/DevOps-Security-Agent-Skills (MIT); frontmatter, When to Use/Limitations, and safety boundaries added for upstream compliance. Docs-only import: helper scripts and templates not bundled.

NetworkPolicy enforcement requires a supporting CNI. The default-deny example also blocks DNS and dependencies until narrowly scoped rules are added; same-namespace pod selectors do not authorize arbitrary namespaces. Test allowed and denied flows from the real source identities and preserve recovery access. readOnlyRootFilesystem may require bounded writable temporary volumes; do not disable it blindly after a startup error. Kubernetes NetworkPolicy behavior.