Clarify goals & constraints
- Multi-tenant Kubernetes with strong isolation, measurable compliance (CIS/PCI), minimal downtime, and reasonable developer velocity.
Node OS baseline
- Use minimal, immutable images (Flatcar, Bottlerocket, Ubuntu minimal). Harden to CIS benchmarks and disable unused services.
- Automate with IaC: Terraform + cloud-init/ignition; configuration managed by Ansible/Chef.
- Patch strategy: automated staged updates with drain/cordon and canary nodes; snapshot AMIs.
Kernel tunables
- Enforce sysctl via kubelet --feature-gates and PodSecurity (for allowed lists) and node-level policies:
- Network: net.ipv4.ip_forward=0, disable packet redirects
- IPC: kernel.shm* limits if needed
- Protect kernel: kernel.randomize_va_space=2
- Use node lockdown (grsecurity/SELinux/AppArmor) and mount options (noexec,nodev,nosuid) for container filesystems.
Container runtime restrictions
- Require modern runtimes (containerd) with default seccomp profile; block dockerd where possible.
- Mandatory:
- Seccomp: apply default-deny with curated allow-lists; use distro seccomp + runtime profiles for privileged workloads.
- Capabilities: drop all, add minimal (CAP_NET_BIND_SERVICE) per need.
- Read-only rootfs with writable volumes for app data only.
- No privileged containers, disallow hostNamespace mounts except approved DaemonSets.
- Enforce via PodSecurityAdmission + runtimeClass constraints.
Pod admission & policy
- Deploy admission controllers: PodSecurityAdmission for baseline/restricted, OPA Gatekeeper or Kyverno for fine-grained policies (labels, seccomp annotated, image repo).
- Example policies: enforce readOnlyRootFilesystem=true, runAsNonRoot, allowedCapabilities empty, seccompProfile present.
Image scanning & signing
- CI pipeline: scan images with Trivy/Clair/Snyk on build, fail on critical CVEs; store SBOM.
- Signing: use cosign/Notary to sign artifacts; admission checks verify signature and provenance.
- Private registry with immutability and trust policies.
Automated enforcement & remediation
- Shift-left: CI gates + policy tests.
- Runtime: admission controllers in control plane; Kyverno can mutate to attach seccomp or labels.
- Continuous compliance: periodic cluster scans (Kube-bench, Polaris), alerting, auto-remediation runbooks (auto-quarantine images, cordon nodes).
- Observability: audit logs to ELK/Datadog, runtime detection with Falco, and automated alert → incident playbooks.
Trade-offs: developer agility vs strict security
- Strict policies reduce risk but slow iteration. Mitigations:
- Provide secure defaults and developer-friendly self-service: templates, Helm charts, mutating admission hooks to inject secure sidecars/profiles.
- Tiered environments: sandbox (developer agility, relaxed policies), staging (enforced scans/signing), prod (strict).
- Exception process: short-lived privileged tickets with approval workflow and automatic expiry.
- Invest in tooling (local policy checks, fast image scanners) to keep feedback loop short.
Measurables & runbook
- Key metrics: time-to-patch, number of non-compliant pods, mean time to remediate, CVE backlog.
- Maintain runbooks for compromises, node rebuilds, and policy exceptions.
This plan balances strong host/runtime hardening, automated enforcement, and developer productivity through tooling, tiers, and well-documented exception paths.
