kubernetes-platform

Acknowledgement: Shared by Peter Bamuhigire, techguypeter.com, +256 784 464178.

Use When

• Standing up a self-managed Kubernetes cluster on Debian/Ubuntu VPS hosts (kubeadm).
• Designing namespace, RBAC, ResourceQuota, LimitRange, and Pod Security boundaries for a multi-team or multi-tenant cluster.
• Owning cluster lifecycle: upgrades, certificate rotation, etcd backup and restore.
• Installing the minimum platform layer above the cluster: ingress controller, cert-manager, metrics-server.
• Choosing between self-managed kubeadm and cloud-managed control planes (EKS, GKE, AKS).

Do Not Use When

• Authoring the application architecture inside the cluster — use microservices-architecture (decomposition models and inter-service communication).
• Provisioning the cluster's underlying VMs, VPC, or DNS through code — use infrastructure-as-code and cloud-architecture.
• Building CI/CD pipelines that deploy into Kubernetes — use cicd-pipelines (pipeline shape and stage-gate design live there).
• Cluster-level observability deep-dives — use observability-monitoring (SigNoz-led observability platform).
• Service mesh design (Istio, Linkerd, Cilium service mesh) — out of scope.

Sibling Kubernetes Skills

This skill is the platform-team angle. Cross-reference rather than duplicate:

• references/kubernetes-fundamentals.md — first cluster, mental model of core objects, kubectl workflow, debug triage.
• references/kubernetes-production.md — Helm release patterns, HPA/VPA, observability stack, troubleshooting playbook.
• references/kubernetes-saas-delivery.md — multi-tenant isolation models, GitOps with ArgoCD, progressive delivery.

Load the sibling that owns a specific topic. This skill owns the bootstrap, governance, security, and lifecycle layer that those skills assume is in place.

Required Inputs

• Target host inventory (control-plane and worker IPs, OS, RAM, CPU).
• Pod and service CIDR plan that does not collide with the host network.
• Tenant or team list for namespace and RBAC design.
• Compliance and data-residency constraints that drive self-managed vs managed.

Inputs

Decision rules

Prerequisite Skills

• cloud-architecture — for the network substrate.
• cicd-pipelines — for the Linux operations baseline on Debian/Ubuntu hosts (Jenkins-on-Debian guidance lives there).
• web-app-security-audit — for baseline application security posture.

Workflow

1. Confirm scope: bootstrap, governance, security, lifecycle, or platform-component install. Route topics owned by sibling skills (references/kubernetes-fundamentals.md, references/kubernetes-production.md, references/kubernetes-saas-delivery.md) to those skills before starting here.
2. Capture inputs: host inventory, CIDR plan, tenant list, compliance constraints.
3. Apply §1–§10 of this skill in order for a green-field cluster, or jump to the relevant section for a targeted change.
4. Load the matching references/<topic>.md file only when the depth is needed.
5. Produce the runbooks listed in Outputs and check them into the platform repo before handing the cluster to tenants.

Quality Standards

• Self-managed kubeadm on Debian/Ubuntu is the default; cloud-managed is the alternative when constraints in §10 flip.
• Every namespace ships with RBAC, ResourceQuota, LimitRange, and a restricted Pod Security label before workloads land.
• Every cluster has an etcd snapshot cron and a documented restore drill. Untested backups do not count.
• Every platform component (ingress, cert-manager, metrics-server, CNI) is version-pinned in platform/versions.yaml.
• Cross-reference sibling Kubernetes skills rather than duplicating their guidance.

§1 Cluster Architecture

Control-plane components (kubernetes.io/docs/concepts/overview/components/, fetched 2026-05-01):

Node components:

For self-managed Debian/Ubuntu clusters, containerd is the default runtime. Verify against the current kubernetes.io container-runtimes page before pinning a version.

§2 Self-Managed Bootstrap on Debian/Ubuntu

The full kubeadm bootstrap flow, kubelet flags, HA control-plane variant, and CNI selection rubric live in references/kubeadm-bootstrap.md. Minimum viable sequence:

# Control-plane node (Debian/Ubuntu, kubeadm + kubelet + containerd installed)
sudo kubeadm init \
  --apiserver-advertise-address=<control-plane-ip> \
  --pod-network-cidr=10.244.0.0/16   # match the chosen CNI

mkdir -p $HOME/.kube
sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
sudo chown $(id -u):$(id -g) $HOME/.kube/config

# Install a CNI (Cilium, Calico, or Flannel) — required for Pod networking
# kubectl apply -f <CNI-manifest>

sudo kubeadm token create --print-join-command

Each worker:

sudo kubeadm join <control-plane-address>:<port> \
  --token <token> \
  --discovery-token-ca-cert-hash sha256:<hash>

Post-init: install the Pod network add-on, label nodes by role, and copy admin.conf to any management workstation. For HA control planes, use InitConfiguration and JoinConfiguration files; pass kubelet overrides through nodeRegistration.kubeletExtraArgs.

CNI choice (Cilium, Calico, Flannel) is left to the implementing team — pick one and pin it; do not mix.

§3 Workloads — Minimum-Viable Manifests

Authoring core workloads is owned by references/kubernetes-fundamentals.md. The platform team still needs a reference for what "compliant by default" looks like, because every tenant manifest is reviewed against it. A Deployment + Service + Ingress that satisfies the restricted Pod Security profile:

apiVersion: apps/v1
kind: Deployment
metadata: { name: web, namespace: app }
spec:
  replicas: 3
  selector: { matchLabels: { app: web } }
  template:
    metadata: { labels: { app: web } }
    spec:
      serviceAccountName: web
      securityContext:
        runAsNonRoot: true
        seccompProfile: { type: RuntimeDefault }
      containers:
        - name: web
          image: ghcr.io/example/web:sha-abc1234
          ports: [{ containerPort: 3000 }]
          resources:
            requests: { cpu: "100m", memory: "128Mi" }
            limits:   { cpu: "500m", memory: "512Mi" }
          readinessProbe: { httpGet: { path: /healthz, port: 3000 }, periodSeconds: 5 }
          livenessProbe:  { httpGet: { path: /healthz, port: 3000 }, periodSeconds: 15 }
          securityContext:
            allowPrivilegeEscalation: false
            readOnlyRootFilesystem: true
            capabilities: { drop: ["ALL"] }
---
apiVersion: v1
kind: Service
metadata: { name: web, namespace: app }
spec:
  selector: { app: web }
  ports: [{ port: 80, targetPort: 3000 }]
---
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: web
  namespace: app
  annotations:
    cert-manager.io/cluster-issuer: letsencrypt-prod
spec:
  ingressClassName: nginx
  tls: [{ hosts: [web.example.com], secretName: web-tls }]
  rules:
    - host: web.example.com
      http: { paths: [{ path: /, pathType: Prefix, backend: { service: { name: web, port: { number: 80 } } } }] }

Probe and lifecycle detail → see references/kubernetes-fundamentals.md §"Probes — Get Them Right". Mental model of Deployments, StatefulSets, Services → references/kubernetes-fundamentals.md §"Core Objects".

§4 Helm

Chart structure and reserved directories (helm.sh/docs/topics/charts, fetched 2026-05-01):

Helm reserves use of the charts/, crds/, and templates/ directories. (helm.sh, fetched 2026-05-01.)

Release lifecycle:

helm repo add bitnami https://charts.bitnami.com/bitnami
helm repo update
helm install web ./charts/web -n app --create-namespace -f values.prod.yaml
helm upgrade web ./charts/web -n app -f values.prod.yaml
helm rollback web 1 -n app
helm uninstall web -n app

Chart authoring patterns (named templates, subchart values overrides, chart testing, schema-validated values) → see references/helm-charts.md. Helm-vs-Kustomize tradeoff → references/kubernetes-production.md §"Helm vs Kustomize".

§5 RBAC

Four object kinds: Role (namespace-scoped), RoleBinding (namespace-scoped), ClusterRole (cluster-scoped), ClusterRoleBinding (cluster-scoped). ServiceAccount is the workload identity. (kubernetes.io/docs/reference/access-authn-authz/rbac/.)

Namespace-admin Role + RoleBinding:

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata: { namespace: team-a, name: ns-admin }
rules:
  - apiGroups: [""]
    resources: ["pods", "services", "configmaps", "secrets"]
    verbs: ["get", "list", "watch", "create", "update", "patch", "delete"]
  - apiGroups: ["apps"]
    resources: ["deployments", "replicasets", "statefulsets"]
    verbs: ["*"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata: { namespace: team-a, name: team-a-admins }
subjects:
  - kind: Group
    name: team-a-admins
    apiGroup: rbac.authorization.k8s.io
roleRef:
  kind: Role
  name: ns-admin
  apiGroup: rbac.authorization.k8s.io

Decision rubric:

Aggregated ClusterRoles, OIDC group mapping, audit patterns, and breakglass identities → references/rbac-patterns.md.

§6 Resource Governance

ResourceQuota enforces aggregate limits per namespace (kubernetes.io/docs/concepts/policy/resource-quotas/, fetched 2026-05-01):

Key behaviour: namespace-scoped, non-retroactive, and once a CPU or memory quota is in force every pod in the namespace must declare matching requests and limits. Over-quota submissions are rejected with HTTP 403.

LimitRange sets default requests/limits and min/max values so authors get sane defaults when they omit them. PriorityClass lets the scheduler preempt low-priority pods to make room for critical workloads.

Quota + LimitRange for a tenant namespace:

apiVersion: v1
kind: ResourceQuota
metadata: { name: team-a-quota, namespace: team-a }
spec:
  hard:
    requests.cpu: "10"
    requests.memory: 20Gi
    limits.cpu: "20"
    limits.memory: 40Gi
    pods: "100"
    persistentvolumeclaims: "20"
---
apiVersion: v1
kind: LimitRange
metadata: { name: team-a-defaults, namespace: team-a }
spec:
  limits:
    - type: Container
      default:        { cpu: "500m", memory: "512Mi" }
      defaultRequest: { cpu: "100m", memory: "128Mi" }
      max:            { cpu: "2",    memory: "4Gi" }

Per-tenant quota sizing, PriorityClass design for system vs workload tiers, and HPA interaction with quotas → references/kubernetes-production.md §"Resource Management".

§7 Pod Security

Three Pod Security Standards profiles, cumulative (kubernetes.io/docs/concepts/security/pod-security-standards/, fetched 2026-05-01):

Enforce by labelling the namespace: pod-security.kubernetes.io/enforce: restricted (verify the exact label key against the current Pod Security Admission docs before applying in production).

Compliant securityContext for restricted:

securityContext:
  runAsNonRoot: true
  runAsUser: 10001
  seccompProfile: { type: RuntimeDefault }
containers:
  - name: app
    securityContext:
      allowPrivilegeEscalation: false
      readOnlyRootFilesystem: true
      capabilities: { drop: ["ALL"] }

NetworkPolicy is the namespace firewall. Default-deny ingress + egress, then allow only what is needed:

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata: { name: default-deny, namespace: team-a }
spec:
  podSelector: {}
  policyTypes: [Ingress, Egress]

Migrating an existing namespace from baseline to restricted, exempting infrastructure namespaces, and warn-vs-enforce strategy → references/pod-security.md.

§8 Cluster Lifecycle

Upgrade flow:

1. kubeadm upgrade plan to see available targets and skew rules.
2. kubeadm upgrade apply v<minor>.<patch> on the first control-plane node.
3. kubeadm upgrade node on the remaining control-plane nodes and on every worker, one at a time, draining before and uncordoning after.

Verify the exact command sequence against the current kubeadm upgrade docs for the target minor version before running in production.

Certificate rotation: kubeadm certs check-expiration and kubeadm certs renew all rotate the kubeadm-issued control-plane certificates. After renewal, restart the static pods (kube-apiserver, kube-controller-manager, kube-scheduler) by removing and re-adding their manifests in /etc/kubernetes/manifests/.

etcd snapshot:

ETCDCTL_API=3 etcdctl \
  --endpoints=https://127.0.0.1:2379 \
  --cacert=/etc/kubernetes/pki/etcd/ca.crt \
  --cert=/etc/kubernetes/pki/etcd/server.crt \
  --key=/etc/kubernetes/pki/etcd/server.key \
  snapshot save /backup/etcd-$(date +%F).db

Schedule the snapshot with cron and ship it to off-host storage. Restore with etcdctl snapshot restore per the upstream etcd docs.

Drain ordering, PodDisruptionBudgets, version-skew rules between kubelet and apiserver, and add-on upgrade order → references/cluster-lifecycle.md. Production-side rolling upgrade playbook → references/kubernetes-production.md §"Cluster and Node Upgrades".

§9 Cluster-Managed Components

Minimum platform layer above a kubeadm cluster (CNI plus the three below):

Pin a version per component, install with Helm or static manifest, and bake the chosen versions into the cluster bootstrap script. Detail on ClusterIssuer patterns, wildcard certs, ingress-class isolation per tenant, and metrics-server TLS flags → references/cluster-managed-components.md.

§10 Self-Managed vs Managed

Lead with self-managed kubeadm on Debian/Ubuntu. Treat managed control planes as the alternative when the constraints below flip:

If two or more "cloud-managed" rows apply, do not self-manage — the operational tax outweighs the sovereignty benefit.

Anti-Patterns

• Running tenant workloads in the same namespace as platform components.
• Granting cluster-admin to a team because RBAC design felt slow.
• Setting CPU limits equal to requests everywhere by reflex — causes throttling under spikes; reserve that pattern for latency-sensitive workloads.
• Enforcing restricted cluster-wide on day one without first running it as warn and fixing offenders.
• Skipping the etcd snapshot cron because "we never had to restore" — the first restore drill is not the day of the outage.
• Mixing two CNIs in one cluster.
• Copy-pasting EKS/GKE manifests into a kubeadm cluster without checking that the storage class, load-balancer class, and IAM assumptions still hold.

Outputs

• A bootstrap runbook for the chosen control-plane and worker layout.
• A namespace, RBAC, ResourceQuota, and LimitRange template per tenant tier.
• A Pod Security enforcement plan with warn → enforce migration steps.
• An upgrade and etcd-backup runbook with rotation and restore drills.
• A pinned-version manifest for ingress controller, cert-manager, and metrics-server.

Companion Skills

• references/kubernetes-fundamentals.md — core objects, kubectl, debug triage.
• references/kubernetes-production.md — Helm release patterns, scaling, observability stack.
• references/kubernetes-saas-delivery.md — multi-tenant isolation, GitOps, progressive delivery.
• cloud-architecture — VPC, load balancers, DNS substrate.
• infrastructure-as-code — Terraform modules that provision the VMs and network.
• cicd-pipelines — pipelines that build and deploy into the cluster (pipeline shape and Jenkins-on-Debian guidance live there).
• observability-monitoring — SigNoz-led observability above the cluster.
• web-app-security-audit — application-layer security for workloads inside the cluster.

References

Tier 1 — Canonical:

• Kubernetes in Action, Marko Luksa, Manning.
• Production Kubernetes, Josh Rosso, Rich Lander, Alex Brand, John Harris, O'Reilly.
• kubernetes.io documentation — https://kubernetes.io/docs/.
• Components page — https://kubernetes.io/docs/concepts/overview/components/.
• kubeadm cluster guide — https://kubernetes.io/docs/setup/production-environment/tools/kubeadm/create-cluster-kubeadm/.
• Pod Security Standards — https://kubernetes.io/docs/concepts/security/pod-security-standards/.
• Resource Quotas — https://kubernetes.io/docs/concepts/policy/resource-quotas/.
• Helm chart docs — https://helm.sh/docs/topics/charts/.

Tier 2 — Supporting:

• ingress-nginx — https://kubernetes.github.io/ingress-nginx/.
• cert-manager — https://cert-manager.io/docs/.
• metrics-server — https://github.com/kubernetes-sigs/metrics-server.

Tier 3 — Supplementary:

• kubeadm upgrade — https://kubernetes.io/docs/tasks/administer-cluster/kubeadm/kubeadm-upgrade/.

Deep-dives in references/:

• kubeadm-bootstrap.md — full bootstrap runbook, HA control plane, CNI selection.
• helm-charts.md — chart authoring patterns, schema validation, subchart overrides.
• rbac-patterns.md — aggregated roles, OIDC group mapping, audit, breakglass.
• pod-security.md — warn to enforce migration, exemptions, NetworkPolicy patterns.
• cluster-lifecycle.md — upgrade ordering, version skew, etcd restore drill.
• cluster-managed-components.md — ingress, cert-manager, metrics-server install patterns.

Evidence Produced