Skill v1.0.0

version: "1.0.0"

agentic-workflows-blueprint.workflow.performing-container-image-hardening

Goal

Harden container images by reducing attack surface, enforcing non-root and immutable runtime constraints, and validating security posture with repeatable checks.

Scope

• Applies to: Docker/OCI image build pipelines and runtime-ready image hardening baselines.
• Does not cover: host daemon hardening or runtime threat monitoring controls.

Triggers

• "Harden container image for production"
• "Reduce image CVE surface"
• "Apply non-root/read-only/container hardening best practices"
• "Implement multi-stage secure Docker builds"

Inputs

• imageBuildContext: Dockerfile/build context and runtime requirements
• baseImageStrategy: minimal/distroless/scratch policy and digest pinning approach
• securityBaseline: required hardening controls (non-root, read-only fs, capability drop)
• validationPolicy: scanner checks and pass/fail thresholds
• runtimePlatform (optional): Kubernetes/container runtime constraints

Invariants

• Production images must avoid unnecessary packages and tooling.
• Images must run as non-root unless explicitly justified.
• Base images should be pinned by digest for reproducibility and trust.
• Security validation must include vulnerability and configuration checks.
• Hardening cannot break application runtime requirements without mitigation plan.

Procedure

1. Assess current image posture

• Measure size, package inventory, and current vulnerability baseline.
• Identify unnecessary build/runtime dependencies.

1. Apply multi-stage build design

• Separate builder and runtime stages.
• Copy only required runtime artifacts into final image.

1. Minimize runtime footprint

• Use slim/distroless/scratch-compatible base strategy.
• Remove unnecessary package managers, shells, docs, and setuid/setgid binaries when feasible.

1. Enforce identity and privilege controls

• Create and run as non-root user/group.
• Configure least-privilege runtime flags and capability drops.

1. Apply filesystem and process hardening

• Design for read-only root filesystem plus explicit writable mounts.
• Add health checks and deterministic entrypoints.

1. Pin trust anchors

• Pin base image by digest.
• Track update cadence for base image refresh.

1. Validate hardening outcomes

• Run vulnerability/config scans and compare before/after posture.
• Verify runtime behavior (non-root, read-only expectations, app liveness).

1. Publish hardening report

• Document posture improvements, residual risks, and deferred remediations.

Outputs

• Hardened Dockerfile/image build spec.
• Before/after hardening report (size and vulnerability delta).
• Validation evidence for non-root, filesystem policy, and scanner results.
• Residual risk register with follow-up actions.

Review gate

• [ ] Final image uses minimized trusted base strategy.
• [ ] Non-root and least-privilege settings are enforced.
• [ ] Read-only/root-hardening controls are validated where applicable.
• [ ] Vulnerability/config checks meet policy thresholds.
• [ ] Hardening changes preserve required application behavior.

References

• ../../SKILL.md
• ../scanning-docker-images-with-trivy/SKILL.md
• ../review/SKILL.md