container-security

Image Scanning

Run Trivy before every push. Fail CI on HIGH or CRITICAL vulnerabilities.

trivy image myapp:latest --severity HIGH,CRITICAL --exit-code 1

Use Grype as a second scanner. Different scanners catch different CVEs.

grype myapp:latest --fail-on high

Store scan results as build artifacts for trending.

trivy image myapp:latest --format json --output scan-results.json

Minimal Base Images

Use distroless or scratch for runtime. Multi-stage builds separate build tools from runtime. See references/dockerfile-hardening.md for complete BAD/GOOD Dockerfile patterns for Go, Node.js, and static binaries.

Rootless Containers

Always create a non-root user and switch to it. For distroless, use the built-in nonroot user (UID 65532). See references/dockerfile-hardening.md for rootless patterns.

Secrets Management

BAD: Baking secrets into the image. They persist in layers even if deleted.

FROM node:24-alpine
ENV DATABASE_PASSWORD=supersecret
COPY . /app
CMD ["node", "server.js"]

GOOD: Inject secrets at runtime via environment variables or mounted files.

docker run -e DATABASE_PASSWORD="$(cat /secure/db-password)" myapp:latest

For Kubernetes, use Secrets mounted as volumes or environment variables.

env:
  - name: DATABASE_PASSWORD
    valueFrom:
      secretKeyRef:
        name: db-credentials
        key: password

Build-Time Secrets

Use BuildKit secrets for credentials needed during build (e.g., private registry tokens).

BAD: Copying .env file into the image.

COPY .env /build/.env
RUN npm install --registry=https://private.npm.com

GOOD: Mount secrets during build without persisting them.

# syntax=docker/dockerfile:1
RUN --mount=type=secret,id=npmrc,target=/root/.npmrc \
    npm install --registry=https://private.npm.com

Build with:

docker buildx build --secret id=npmrc,src=.npmrc .

Audit .dockerignore

Ensure secrets never enter the build context.

.env
.env.*
*.key
*.pem
secrets/
credentials.json

Scan committed Dockerfiles for hardcoded tokens.

gitleaks detect --source . --no-git

Supply Chain Security

Sign Images with Cosign

Sign after building. Verify before deploying.

cosign sign myregistry.com/myapp:v1.0.0

Verify signature before pull.

cosign verify --key cosign.pub myregistry.com/myapp:v1.0.0

Generate SBOM

Create a Software Bill of Materials for every release.

syft myapp:latest -o json > sbom.json
trivy image --format cyclonedx --output sbom.json myapp:latest

Attach SBOM to the image as an OCI artifact.

cosign attach sbom --sbom sbom.json myregistry.com/myapp:v1.0.0

Pin Dependencies by Digest

BAD: Using mutable tags. Tags can be overwritten.

FROM node:24-alpine

GOOD: Pin by digest. Digest is immutable.

FROM node:24-alpine@sha256:abc123...

Find digests with:

docker pull node:24-alpine
docker inspect node:24-alpine | jq -r '.[0].RepoDigests[0]'

Runtime Policies

Admission control (Gatekeeper, Kyverno), seccomp profiles, and Falco runtime monitoring. See references/runtime-security.md for policy YAML examples and Falco rules.

CI Checklist

1. Lint Dockerfile with Hadolint.

hadolint Dockerfile

2. Scan for secrets in build context.

gitleaks detect --source . --no-git

3. Build and scan image.

docker build -t myapp:latest .
trivy image myapp:latest --exit-code 1 --severity HIGH,CRITICAL

4. Sign image and generate SBOM.

cosign sign myregistry.com/myapp:v1.0.0
syft myapp:latest -o json > sbom.json

5. Push to registry with immutable tag.

docker tag myapp:latest myregistry.com/myapp:v1.0.0
docker push myregistry.com/myapp:v1.0.0

6. Verify signature before deploying.

cosign verify --key cosign.pub myregistry.com/myapp:v1.0.0

Dockerfile Best Practices

Complete BAD/GOOD Dockerfile comparisons and common mistakes. See references/dockerfile-hardening.md for full examples.