Container Hardening

Secure container images and runtime configurations.

When to Use This Skill

Use this skill when:

• Building secure container images
• Hardening container deployments
• Meeting container security requirements
• Implementing defense in depth

Dockerfile Security

# Use minimal base image
FROM alpine:3.18

# Don't run as root
RUN addgroup -g 1001 -S appgroup && \
    adduser -u 1001 -S appuser -G appgroup

# Copy with specific ownership
COPY --chown=appuser:appgroup . /app

# Remove unnecessary packages
RUN apk del --purge build-dependencies && \
    rm -rf /var/cache/apk/*

# Use non-root user
USER appuser

# Read-only filesystem support
WORKDIR /app

Runtime Security

# Run with security options
docker run -d \
  --read-only \
  --tmpfs /tmp \
  --security-opt=no-new-privileges:true \
  --cap-drop=ALL \
  --cap-add=NET_BIND_SERVICE \
  --user 1001:1001 \
  myapp:latest

Kubernetes Security Context

apiVersion: v1
kind: Pod
spec:
  securityContext:
    runAsNonRoot: true
    runAsUser: 1001
    fsGroup: 1001
  containers:
  - name: app
    securityContext:
      allowPrivilegeEscalation: false
      readOnlyRootFilesystem: true
      capabilities:
        drop: ["ALL"]

Image Scanning

# Scan with Trivy
trivy image --severity HIGH,CRITICAL myapp:latest

# Use distroless images
FROM gcr.io/distroless/static-debian11

Best Practices

• Use minimal base images
• Run as non-root user
• Enable read-only filesystem
• Drop all capabilities
• Scan images regularly
• Sign and verify images
• Use secrets management

Related Skills

• container-scanning (container-scanning) - Vulnerability scanning
• kubernetes-hardening (kubernetes-hardening) - K8s 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.