Kubernetes Manifest Review

Kubernetes Manifest Review

Purpose

Conduct a structured review-and-author pass over Kubernetes manifests, Kustomize overlays, or Helm charts — covering resource requests/limits, liveness/readiness/startup probes, pod and container security context, RBAC least privilege, NetworkPolicy isolation, autoscaling (HPA), secret handling, and reliability anti-patterns. The goal is workloads that schedule predictably, fail safely, run unprivileged, and expose the minimum surface. Findings must come from the actual YAML and a server-side dry-run, never from assumptions, and nothing is applied to a live cluster without human approval.

When to use

• A PR adds or changes manifests under k8s/, manifests/, deploy/, a Helm templates/ dir, or values.yaml.
• Pods are OOMKilled, CPU-throttled, evicted, or crash-looping due to missing limits/probes.
• A Deployment, StatefulSet, DaemonSet, Service, Ingress, RBAC, or NetworkPolicy is being introduced.
• Containers run as root, privileged, or with broad RBAC and you need a security pass.
• Autoscaling or rollout behavior needs review before a release.

When not to use

• The change is application code only, with no manifest or chart change.
• The cluster uses a different orchestrator (Nomad, ECS) — adapt principles, not commands.
• The task is a production incident needing an emergency rollout — escalate to a human operator.

Procedure

1. Orient to the manifests

find . -path "*/k8s/*" -o -name "*.yaml" -path "*manifests*" 2>/dev/null
grep -rln "^kind:" . --include="*.yaml" | head
grep -rhE "^kind:" . --include="*.yaml" | sort | uniq -c   # inventory of object kinds

2. Validate structure without touching the cluster

# Client-side validation only — no cluster mutation
kubectl apply --dry-run=client -f manifests/ 2>&1 | tail -20
# Stronger static schema validation if available
kubeconform -strict -summary manifests/ 2>/dev/null || echo "kubeconform not installed"
# Render Helm to inspect the real output
helm template ./chart -f chart/values.yaml > rendered.yaml 2>/dev/null

3. Check resource requests and limits

# Containers missing requests/limits are unschedulable-safe risks (noisy-neighbor, OOM)
grep -rL "resources:" manifests/ --include="*.yaml"
grep -rn "requests:\|limits:\|memory:\|cpu:" manifests/ --include="*.yaml"

4. Check probes

grep -rn "livenessProbe\|readinessProbe\|startupProbe" manifests/ --include="*.yaml"
# Workloads with containers but no readinessProbe send traffic to unready pods

5. Audit security context and RBAC

# Pod/container security context
grep -rn "runAsNonRoot\|runAsUser\|allowPrivilegeEscalation\|readOnlyRootFilesystem\|privileged\|capabilities" manifests/ --include="*.yaml"
# RBAC wildcards (over-permission)
grep -rn "verbs:\|resources:\|apiGroups:" manifests/ --include="*.yaml"
grep -rn "\"\*\"\|- '\*'\|- \"\*\"" manifests/ --include="*.yaml"
grep -rn "kind: ClusterRoleBinding" manifests/ --include="*.yaml"  # prefer namespaced RoleBinding

6. Check network policy, secrets, and autoscaling

grep -rln "kind: NetworkPolicy" manifests/ --include="*.yaml" || echo "no NetworkPolicy — default-allow traffic"
# Secrets must not be inline plaintext literals in manifests
grep -rn "kind: Secret" -A6 manifests/ --include="*.yaml"
grep -rn "stringData:\|data:" manifests/ --include="*.yaml"
grep -rln "kind: HorizontalPodAutoscaler" manifests/ --include="*.yaml"

Concrete checks

• Every container sets CPU and memory requests and limits.
• Every long-running service container has a readinessProbe and a livenessProbe; slow starters use a startupProbe.
• Pod security context sets runAsNonRoot: true and a non-zero runAsUser.
• Container security context sets allowPrivilegeEscalation: false, readOnlyRootFilesystem: true, and drops ALL capabilities.
• No container runs privileged: true or mounts the host network/PID/filesystem without justification.
• RBAC uses namespaced Role/RoleBinding where possible; no verbs/resources/apiGroups: ["*"] ClusterRoles.
• A NetworkPolicy restricts ingress/egress for sensitive workloads (default-deny baseline).
• Secrets are referenced via secretKeyRef/envFrom, not hardcoded plaintext in manifests.
• An HorizontalPodAutoscaler (or documented fixed replica count) governs scaling.
• Deployments set strategy (RollingUpdate with sane maxUnavailable/maxSurge).
• A PodDisruptionBudget protects multi-replica services during node drains.
• Image tags are pinned (not :latest) with imagePullPolicy consistent with the tag.

Commands or Templates

# Hardened Deployment container spec — review target
apiVersion: apps/v1
kind: Deployment
metadata: { name: api, namespace: prod }
spec:
  replicas: 3
  strategy:
    type: RollingUpdate
    rollingUpdate: { maxUnavailable: 0, maxSurge: 1 }
  template:
    spec:
      securityContext:
        runAsNonRoot: true
        runAsUser: 65532
        seccompProfile: { type: RuntimeDefault }
      containers:
        - name: api
          image: registry.example.com/api:1.4.2   # pinned, not latest
          resources:
            requests: { cpu: "100m", memory: "128Mi" }
            limits:   { cpu: "500m", memory: "256Mi" }
          readinessProbe:
            httpGet: { path: /healthz, port: 8080 }
            initialDelaySeconds: 5
          livenessProbe:
            httpGet: { path: /livez, port: 8080 }
            periodSeconds: 10
          securityContext:
            allowPrivilegeEscalation: false
            readOnlyRootFilesystem: true
            capabilities: { drop: ["ALL"] }
          envFrom:
            - secretRef: { name: api-secrets }   # not inline plaintext

# Default-deny NetworkPolicy baseline
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata: { name: default-deny, namespace: prod }
spec:
  podSelector: {}
  policyTypes: ["Ingress", "Egress"]

# Safe review commands — never mutate the cluster
kubectl apply --dry-run=client -f manifests/   # client-side only
kubeconform -strict -summary manifests/
helm template ./chart | kubeconform -strict -summary -

Common issues & anti-patterns

• No resource limits — one pod starves the node; no requests — the scheduler misplaces pods.
• No readiness probe — traffic hits pods before they are ready, causing 5xx during rollout.
• Liveness probe pointed at a slow/expensive endpoint — healthy pods get killed in a loop.
• runAsNonRoot absent and containers run as UID 0; privileged: true "to make it work".
• ClusterRole with ["*"] verbs/resources bound to a workload ServiceAccount.
• No NetworkPolicy — every pod can talk to every other pod (lateral movement risk).
• Plaintext secrets committed in a Secret manifest (base64 is encoding, not encryption).
• image: app:latest — non-reproducible rollouts and broken rollbacks.

Required output

Produce a structured report with:

1. Inventory — object kinds and counts; validation/dry-run result.
2. Resources — containers missing requests/limits.
3. Probes — missing readiness/liveness/startup probes per workload.
4. Security context — root/privileged containers; missing hardening fields.
5. RBAC & network — wildcard roles, ClusterRoleBindings, missing NetworkPolicy.
6. Secrets & scaling — plaintext secrets (redacted); HPA/PDB/strategy presence.
7. Findings table — file:line | issue | severity | concrete fix.
8. Next safe action — highest-priority change before any apply.

Safety

• This is a review and authoring skill. NEVER run kubectl apply (server-side), kubectl delete, kubectl scale, kubectl rollout, kubectl drain/cordon, or helm install/upgrade/uninstall against a real cluster without explicit human approval.
• Only --dry-run=client, kubeconform, and helm template are safe to run unattended — they do not touch the cluster.
• Never put real secret values into a manifest; reference a secret manager, sealed secret, or external secret operator.
• Base64 in a Secret is not encryption — redact discovered secret values to **** and flag for rotation.
• Do not change RBAC bindings, namespaces, or finalizers in ways that could lock out operators without sign-off.
• If a change would delete a StatefulSet, PVC, or namespace, stop and require explicit human approval.